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. . Elements of . . 



Vegetable Microscopy, 



: BY : : 



DANIEL BASE 




VjZV&Z 



. . ELEMENTS OF 



Vegetable Microscopy 



FOR THE USE OF ... . 
STUDENTS OF PHARHACV. 



Preparatory to the Study of Pharmacognosy. 

ILLUSTRATED WITH JO FIGURES. 



BY 



DANIEL BASE, PH. D., 



. . . OF THE . 



. . Maryland College of Pharmacy, 



BALTIMORE, MD. 
1897. 




5^1 DS^^ 






Entered according to Act of Congress, in 

the year 1897, by 

Daniel Base, 

in the Office of the Librarian of Congress 

at Washington. 







PREFACE. 



This little book is intended to serve as a guide for beginners in the 
study of plant tissues with the microscope, with supplemental instruc- 
tion from the teacher. 

The greater portion deals with the tissues and their arrangement 
in the higher plants, but it was thought advisable to introduce a few 
lessons on the simplest plants, viz., some of those of the thallophyte 
series, not only on account of their great importance in the life econ- 
omy, but also to show the gradual increase in complexity of structure 
in passing from the extremely simple and minute plants of the thallo- 
phyte series to the complicated highly organized members of the pha- 
nerogams, thus giving the student a complete view of the structure and 
characteristics of the whole range of the vegetable kingdom. 

The knowledge of the tissues of the higher plants gained in this 
book, which may be designated as the Junior Course in Microscopy, 
will find practical application in the recognition of official vegetable 
drugs, the detection of adulterations, the study of ground drugs and 
their adulterations. This branch of study is called Pharmacognosy 
and is daily increasing in importance. 

The opening pages deal with a few physical principles and a de- 
scription and explanation of the action of a compound microscope, its 
defects, the requirements of a good instrument, etc. The author is 
well aware that it is possible for one to work with a microscope without 
understanding its action, just as a man may know how to start and 
stop an engine without knowing anything of its mechanism and 
theory of action. But it needs no argument to convince anyone that a 
student who knows the theory and structure of a microscope is far 
better equipped than one who merely knows how to bring an object 
into focus and look at it. For this reason, the subject matter in the 
beginning of the book was introduced. 



The matter contained in these pages is the outcome of the author's 
needs in his classes in microscopy. No one book was found entirely 
satisfactory. All contained valuable material but lacked other matters 
which were desirable. Some were too extensive for use in an elemen- 
tary course. In preparing these pages, the author consulted a number 
of books, to which he desires to acknowledge his indebtedness. The 
books consulted were : — Encyclopedia Britannica ; Ganot's Physics; 
Behrens' Botanische Mikroskopie ; Bessey's Botany ; Goodale's Physi- 
ological Botany ; Bastin's College Botany and Lab. Exercises ; Bower's 
Practical Botany ; Huxley and Martin, Practical Biology ; Gray's Les- 
sons in Botany. 

D. B. 
Sep , 1897. 



CONTENTS 



THE MICROSCOPE 

CHAPTER I. 



PAGE. 



Preliminary consideration of light rays, plane and spher- 
ical mirrors, refraction, index of refraction, prism, dis- 
persion, lenses, formation of images by lenses, . . i-5 

Spherical and Chromatic Aberrations, achromatic and 

aplanatic lenses, ...... 5-6 

Simple microscope, distance of most distinct vision, measure 

of magnification, ...... 6-7 

Compound microscope, description of parts, condenser 
(Abbe's), illumination, objectives, dry and immersion 
objectives, angular aperture of lenses, . . 7-9 

Oculars, Huyghens' ocular, positive and negative oculars, 
method of changing oculars and objectives, tube length, 
camera lucida, determination of magnifying power, 
stage micrometer, source of light, . . ... 9-10 

Requisites of a good microscope — Working distance, focal 

depth, flatness of field, defining power, resolving power, 11 

Care of microscope and directions for using same, accessory 

apparatus, ....... n-13 

VEGETABLE HISTOLOGY. 



CHAPTER II. 
Lesson I. — Linen, Cotton, Silk and Wool, . . . 13-14 

CHAPTER III. 
Lesson II.— Yeast Plant (Torula), . , . 14-16 



CHAPTER IV. 

Lesson III.— Bacteria, . . . . . 16-18 

CHAPTER V. 
Lesson IV.— Spirogyra, ..... 19-20 

CHAPTER VI. 
Reproduction, . . . . . . 20-21 

CHAPTER VII. 
Lesson V. Moulds, ...... 21-24 

CHAPTER VIII. 
Tissues of Higher Plants. Lesson VI.— Typical Cell, 24-26 

CHAPTER IX. 
Permanent and Temporary Staining Fluids, fixing and 
hardening reagents, softening reagents, clearing rea- 
gents, permanent and temporary mounting media, 
other micro-reagents, preserving fluids, section cutting, 
operations involved in making a permanent mount, 
scheme for making a permanent mount, . . 27-34 

CHAPTER X 
Lesson VII.— Tissues of Higher Plants, » . 34~37 

CHAPTER XL 
Lesson VIIL— Parenchyma Tissue, .... 37-38 

CHAPTER XII. 
Lesson IX. — Collenchyma, ..... 38-39 

CHAPTER XIII. 
Lesson X. — Sclerotic Cells, ..... 39-40 

CHAPTER XIV. 
Lesson XL — Epidermal Tissue, .... 40-42 

CHAPTER XV. 
Lesson XII.— Epidermal Appendages, . ... 42-43 

CHAPTER XVI. 
Lesson XIII. — Starches. . . . . . 43-46 

CHAPTER XVII. 
Lesson XIV.- Aleurone Grains, .... 46-47 

CHAPTER XVIII. 
Lesson XV.— Chlorophyll Bodies, ... 48 



CHAPTER XIX. page. 

Lesson XVI. — Secretion Sacs, Intercellular Air Spaces 

and Secretion Reservoirs, . . 48-51 

CHAPTER XX. 
Lesson XVII. — Wood and Bast Fibres, . . 5i~54 

CHAPTER XXI. 
Lesson XVIII. — Tracheary Tissue, .... 54-56 

CHAPTER XXII. 
Lesson XIX.— Latex Tissue, .... 56-58 

CHAPTER XXIII. 
Lesson XX. — Vasal Bundles, ..... 58-63 

CHAPTER XXIV. 
Lesson XXI. — Leaves, ..... 63-65 

CHAPTER XXV. 
More Important Test Reactions of the Parts of Vege- 
table Cells. ..... 65-66 

Followed by 15 Pages Containing 70 Figures. 



V 



ELEMENTS OF 

VEGETABLE MICROSCOPY. 



THE MICROSCOPE. 

CHAPTER I. 
Preliminary Considerations. 

Before describing the mechanical and optical parts of a com- 
pound microscope, it is essential to know something about the action of 
transparent bodies, as lenses, prisms, etc., on light rays, — how a lens 
forms an image of an object, and how the image is magnified etc., 
in other words, a little of the elementary physics of light. 

Light travels through homogeneous media, as air, water, glass, in 
straight lines, and a very narrow cylinder of light is called a ray, or 
better, a. pencil of light. Rays are represented in geometric illustra- 
tions by straight lines. The fact that light travels in straight paths may 
easily be shown by admitting a small beam through a hole in a shutter 
into a darkened room in which dust particles are floating around. 
When the rays come, from a distant source, as the sun, moon, stars, a 
distant flame, they are practically parallel, and a beam of such light is 
spoken of as parallel light or beam. {See figure i.) 

A convergent beam of light is one in which the rays come to- 
gether in a point or focus. {See figure 2.) 

A divergent beam of light is one in which the rays emanate from 
a point or focus. {See figure 3.) 

Mirrors : — Perfectly plane surfaces (such as are commonly spoken 
of as smooth surfaces,) turn back or reflect rays of light which fall 
upon them. Such surfaces are called plane mirrors, and are sometimes 
used for illuminating objects on the stage of the microscope. {See fig- 
ure 4.) AB=surface of mirror, CD=a perpendicular to AB. OD is 
called an incident ray and the angle ODC the angle of incidence. DP 
is the reflected ray and CDP, the angle of reflection. In plane mirrors, 
the angle of incidence is always equal to the angle of reflection, and 
hence a beam of parallel rays is reflected in the same parallel condition 
and a divergent beam remains divergent after reflection. {See figures 
5 and 6.) 



2 Elements of Vegetable Microscopy. 

Spherical Mirrors:— These are spherical reflecting surfaces and 
they behave differently from plane mirrors towards rays of light. In 
concave spherical mirrors, parallel rays are made to converge nearly 
to a point after reflection, and in this way the intensity of the light 
is increased. The place where the rays come together is called the 
focus, and a small object placed there would be intensely illumi- 
nated. {See figure 7.) A parabolic mirror brings parallel rays of light 
to a single point or focus, acting thus more perfectly than a spherical 
mirror. These two kinds of mirrors are used much more often on 
microscopes than plane mirrors. 

Refraction ; — It was noted above that a light ray travels in a straight 
line. This is true only when the medium remains the same. Light 
passing from one medium to a different medium, is bent out of its 
course, still moving however in a straight path in the second medium 
but in a different direction from that in the first. The bending of light 
rays is known as Refraction, and the action of microscopes depends on 
this important property. 

To illustrate, let AB be the surface {figure 8.) of separation between 
air and glass ; NS, a perpendicular to AB. CD is an incident ray, DP is 
the direction of the ray after being bent out of its original course CDH, 
i.e., it is the refracted ray. CDN=angle of incidence, PDS==angle of 
refraction. The amount of bending varies for different media, (air being 
taken as the standard,) but is constant for the same medium. The ray 
of light passing from air to any denser medium, is always bent toward 
the perpendicular NS, so that the angle of incidence is greater than 
the angle of refraction. The constancy of the amount of deviation of 
the refracted ray in the same medium is expressed by the law of 
refraction, viz., the ratio of the sine of the angle of incidence to the 
sine of the angle of refraction is a constant quantity It is expressed 
mathematically thus S ine angle CDN _ n & constant# 
Sine angle PDS 

This ratio n, is called the index of refraction of any given medium, 
and is always taken with reference to air as standard. There is only 
one position in which light is not bent out of its path in passing from air 
to any other medium, viz., when the light rays are perpendicular to the 
surface of separation of the two media. In this case the rays pass on 
unbent in the same straight line as shown, {figure 9.) The index of re- 
fraction of water and glass are n=i.33 water, n=i.52 glass (crown). 
Substances for which n is greater than unity, are said to be more re- 
fracting than air. The refractive index has reference to light of on e 
color only i. e., to monochromatic light. A familiar illustration of re- 
fraction is shown by dipping a stick obliquely in water, when it will 
appear bent. 

Refraction through a Prism : — A prism is any transparent medium 
comprised between two plane faces inclined to each other. The inter- 
section of the two plane faces is called the edge and their inclination 
is called the refracting angle. Triangular glass prisms are generally 



Elements of Vegetable Microscopy . 3 

used. (See figure 10.) ABC is a section of such a prism. A is called 
the summit and BC the base. A ray of light DI falling on a prism, as 
in the figure, will not pass through in a straight line DIN, but is twice 
bent out of its course, in accordance with the law of refraction and 
emerges finally as the ray SP. The amount of bending depends on the 
angle of the prism, its material and the angle of incidence of the ray. 
Moreover, light rays of different colors are bent different amounts, since 
the refractive indices for the various colors of light are different. White 
light is a combination of numerous colors and if a beam of sunlight falls 
on a prism it does not come through as white light, but the constituent 
colors are refracted by different amounts, giving rise to a band of light 
containing all the colors of the rain-bow, viz., red, orange, yellow, green, 
blue, indigo, violet, red being least refracted, violet most. {See figure 
ii.) Such a band of colors is known as a spectrum. An instrument has 
been constructed for conveniently observing the spectrum of white light 
which is known as the Spectroscope. It has proved to be of the greatest 
value in chemical analysis. Many new elements were discovered by its 
aid, for ex., calcium, rubidium, thallium, indium, gallium and others. 

The separation of the various colors, due to the unequal refrangi- 
bility of the differently colored rays, is known as dispersion. We shall 
speak again of the unequal refrangibility of differently colored rays 
in connection with lenses and one of their defects, known as chromatic 
aberration. 

Lenses: — A lens is a transparent medium, which, in virtue of its 
curved surfaces, has the property of converging or diverging rays of 
light that fall on it. Lenses used in optics are always spherical or ap- 
proximately so. They are made either of crown or flint glass, the 
former contains no lead, the latter does, and is more refractive than 
crown glass. There are six kinds of lenses as shown in figure 12. 

The first three are thicker in the middle than on the edges and 
have the power of converging light rays to a point, the last three are 
thinner in the middle than on the edges, and diverge light rays ; the 
first are called converging lenses, the latter diverging lenses. 

It will suffice to consider the properties of a biconvex and a bicon- 
cave lens, and what is said about these will apply to the others of the 
same class. 

Biconvex Lens : — The faces, ADB and ANB (figure 13.) of a bicon- 
vex lens are spherical and their centres of curvature are C and C' re- 
spectively, which may or may not be equally distant from the centre O. 
Usually they are equally distant. The line joining C and C' is called 
the optical axis or principal axis. 

If a beam of parallel rays of light falls on the lens as shown in fig- 
ure, the rays will be converged to a point C', called the principal focus 
(burning point), which in a lens of crown glass coincides very nearly 
with the centre of curvature C'. Of course, there are two foci, one on 
each side of the lens, and the distance C'D of the focus from the lens is 
called the focal distance or length. This distance varies with the index 



4 Elements of Vegetable Microscopy. 

of refraction of the glass and the radius of curvature of the faces. The 
shorter the radius of curvature, i.e., the thicker the lens, the shorter 
the focal length. 

Biconcave Lens : — This is just the reverse of the biconvex lens, the 
spherical surfaces bulge inward instead of outward, and it diverges or 
scatters rays of light that fall upon it. {Figure 14.) 

It has two radii of curvature and a principal axis just as in a bicon- 
vex lens. A beam of parallel light is diverged, but if the rays were pro- 
longed backward they would meet in a point or focus as shown in the 
figure. The light after passing through would seem to an eye to come 
from a point C. This is called a virtual or imaginary focus because 
the rays do not actually meet, but only seem to emanate from it, while 
in a convex lens the rays actually meet in a point, which is therefore 
called a real focus. 

Formation of an image by double convex lens : — Without going into 
reasons and geometric construction, the following is the fact, -That if 
a small object be placed near the principal focus but a little distance 
in front of it, the image formed is at a great distance, is inverted and 
much larger, and that in proportion as the object is near the principal 
focus. This is shown in figure 15 where the arrow A represents a 
bright body and the arrow B its inverted image, much larger and at a 
great distance. C is the focus, the body being a little beyond it. The 
rays of light coming from every point of A, are converged by the lens to 
a corresponding point in the image B, and the latter is real and can be 
caught on a screen held at B. The figure represents what takes place 
in a compound microscope as will be shown later. The object and 
image have the same proportion as their distances from the lens. 

If the object is very near the focus but between it and the lens, the 
rays from the various points of the object are not converged to a corre- 
sponding point as in the previous case, but pass through the lens still 
more diverging and in such a way that if they were prolonged back- 
ward they would meet and form an image behind the object on the 
same side of the lens as the latter. Figure 16. will illustrate. An eye 
held in front of the lens would see the light coming from the object A 
as if it came from B, and B therefore is the image of A, erect, larger but 
unreal or imaginary. 

The lens magnifies the object, and the magnification is greater in 
proportion as the lens is more convex and the object nearer the focus. 
As the convexity of a lens increases, the focal length decreases. 

The magnifying action of a lens may also be increased by combin- 
ing two or three lenses, one behind the other, into a "system." A 
lens used, as described, for increasing the size of an object, constitutes 
a simple microscope. 

Formation of an image by a double concave lens : — No real image is 
ever formed by a concave lens ; it is always virtual, erect, and smaller 
than the object, and nearer the lens than the object. If A be an object 
{figure //.), the rays of light from it passing through the lens, will ap- 
pear to the eye to come from B, and hence B is the virtual image of A. 



Elements of Vegetable Microscopy. 

Spherical and Chromatic Aberrations : — There are two serious in- 
herent defects in all simple lenses, known as spherical and chromatic 
aberrations. These defects are detrimental to the formation of a 
perfect image of an object and must be approximately overcome in 
compound microscopes if these are to be of any value at all. 

Cause of Spherical Aberration : — It was said above, that parallel 
rays of light falling on a double convex lens are converged to a point* 
but this is not quite true. The rays falling on the edge of the lens 
are brought to a focus sooner than those rays falling near the centre of 
of the lens, so that the rays instead of coming together at a single point, 
are focused over a small circle. The diagram {Figure /Sj will illustrate. 
The rays around the axis of the lens will meet in a focus F while those 
near the edge will meet in F/ and a screen placed at F will not receive 
a mere point of light as would be the case if the lens were perfect, but 
a small circle of light. The result of this is that the image of any ob- 
ject is not sharply denned but is somewhat blurred in such a manner 
that if the centre of the image is sharp, the edge is indistinct and if the 
edges are sharp, the centre is indistinct. This defect is due to the 
spherical nature of the lens, hence its name. As the edge rays are 
most effective in causing this aberration, the latter can be greatly cor- 
rected by cutting out the edge rays by means of a diaphragm, or per- 
forated disc, placed in front of the lens, (Figure 19.) This is done in 
objectives of compound microscopes. 

Mathematical calculation has shown that spherical aberration is 
greatly reduced when the radii of curvature of a lens bear a certain 
ratio to each other, viz., 6 : 1, the face with longer radius being turned 
towards the object. Aberration is also corrected, in part, by combin- 
ing several lenses of suitable curvatures into a system, the lens next 
the object being plano-convex, with the plane face towards the object. 
(Absolute correction for spherical aberration is impossible.) 

Cause of Chromatic Aberration : We have seen that rays of dif- 
ferent colors have different indices of refraction, i. e., unequal refrang- 
ibilities, so that if white light is passed through a prism, the constitu- 
tuent colors are separated by it into a spectrum. A lens acts like a 
prism in this respect, in fact, it may roughly be considered as two prisms 
with their bases together as shown in figure 20. There is a different 
focus for each of the seven different colors composing white light ; 
violet being most refracted, is focused nearest the lens, while red, be- 
ing least refracted, is focused farthest from the lens. The red rays will 
meet at R the violet ones at V, and the other colors at points interme- 
diate, in the order, orange, yellow, green, blue, indigo, (figure 21.) 
The result of this defect is that the image of an object is bordered by 
a color fringe instead of being perfectly colorless as it should be. Chro- 
matic aberration is more perceptible in proportion as the lenses are 
more convex, i.e., as the magnifying power increases. It is corrected 
by combining lenses made from crown and flint glass. The refractive 
indices of these are very nearly the same, being 1.751 for flint and 1.53 



6 Elements of Vegetable Microscopy. 

for crown, but the power to separate the colors of white light is nearly 
twice as great for flint as for crown glass. Hence a biconcave or plano- 
concave flint glass may be so combined with a biconvex crown glass 
that the dispersion of one is corrected or compensated by that of the 
other, while the two still act like a double convex lens in magnifying 
the object {see figure 22.) Chromatic aberration cannot be corrected 
absolutely ; there will always be a little color, but it may be so little 
that the image is practically colorless. For optical purposes, the blue 
and orange are corrected or combined. If the image is bordered by a 
light blue fringe, the lens is said to be overcorrected, if by a reddish 
one, it is under corrected. 

A lens free from chromatic aberration is called Achromatic, and one 
free from both spherical and chromatic aberrations is called Aplanatic. 

Simple Microscope : — This is nothing but a convex lens used as a 
magnifier as described on page 4, under double convex lens. There may 
be one lens or several combined into a system, and mounted in a suitable 
stand. Corrected lenses and diaphragms may be used to get rid of 
spherical and chromatic aberrations. A good example of a simple 
microscope is a reading glass, or a watchmaker's magnifier. 

Condition of distinctness of the image : — There is for each person a 
distance of most distinct vision, a distance at which an object must be 
placed before the eye, to be seen with greatest distinctness. This dis- 
tance is for the average eye between 12 and 14 inches. It differs for 
different observers and the two extremes are found in near and far 
sighted persons. When an object is looked at through a lens, the 
latter must be moved back and forth until the image is formed at the 
particular observers distance of distinct vision, and this operation is 
called focusing: This explains why two persons looking through a 
microscope will have quite different foci, since the two eyes have 
different distances of distinct vision. 

Measure of Magnification in a simple Microscope : — The apparent 
magnitude of an object is the angle it subtends at the eye of the obser- 
ver, {figure 23.) Angle ACB is the apparent magnitude of the body 
AB. In the case of two objects seen at the same distance, the ratio 
of the apparent diameters is the same as that of their absolute magni- 
tude. Hence, in a simple microscope, (also in a compound one), the mag- 
nification is equal to the ratio of the apparent diameter of the image to 
that of the object, both being at the distance of most distinct vision. 
But as the apparent diameters are not easy to measure, a simpler 
method is used which gives an approximate measurement, {figure 24). 
AB is an object and A / B / its image, formed at the distance of distinct 
vision for the eye E. Since the eye is always very close to the lens, 
the angles subtended by the object and image may be taken as A / OB / 

A / OB / , 

and a Ob and the magnification= This is approximately 

aUb. 

A'B' A'B', A / B / 

equal to ab == AB anc * ^Y similar triangles, a B = 



Elements of Vegetable Microscopy. 7 

DO (dist. of distinct vision) 12 to 14 inches . , ,. . 

— jr-7 — t^t- — z~7 1 ^ ^^ , r n -r\, since the object is very 

dist. of object from lens, FO (focal length)' J 

nearly at the focus. Hence, magnification of a convex lens=ratio of 

distance of distinct vision (say 13 inches as average) to the focal length 

of the lens. It will be seen that magnification is greater as the focal 

length is smaller and as the observer's distance of distinct vision is 

greater. 

COMPOUND MICROSCOPE. 

The simplest form would consist of two simple microscopes or 
magnifiers, one with short focus, placed near the object, called the 
objective, the other with longer focus, placed next the eye and 
called the eyepiece or power. The objective forms an inverted real im- 
age of the object, and by means of the eyepiece, we see a virtual erect 
magnified image of the real image. 

Mode of action : — {In figure 23.) AB is an object ; an image is formed 
at ab, real inverted and magnified. The eyepiece forms an imagi- 
nary, erect, magnified image of ab at A / B / . This is the principle of all 
compound microscopes. This form would be very defective on account 
of spherical and chromatic aberrations and we will now study the more 
perfect microscope. 

Description of Compound Microscope : — {Figure 26.) A, base; B, 
pillar ; C, pillar and arm ; D, body ; E, nose-piece ; F, objective ; G, ocu- 
lar ; H, draw- tube ; I, collar ; J, rack and pinion ; K, coarse adjustment ; 
L, fine adjustment ; N, spring clips ; O, mirror ; P, mirror bar ; Q, dia- 
phragm and substage ; R, substage screw; S, stage; T, pillar hinge- 
joint. 

Only a few words need be said about the mechanical parts of the 
instrument as the figure will explain sufficiently. 

By the rack and pinion movement K, the body D is given a large 
up and down motion and a body is quickly brought into rough focus. 
Then by the micrometer screw L the fine adjustment is made, a very 
small motion of the body D being produced by one turn of the screw. 

The draw tube H carries a scale so that any tube length can be 
obtained by pulling out or pushing in. The ocular G slips into the end 
of the tube H. The triple nose-piece E is a convenience for sliding one 
or the other objective into place as desired. The stage is perforated in 
the centre for transmitting light, reflected up by the mirror O. In the 
opening there may be fitted little cylinders with smaller openings, 
known as diaphragms, the object of which is to regulate the amount of 
light, {figure 27.) There is a series of three or four of these. On the 
stage are two clips for holding a glass slide on which the object is 
examined. 

The iris diaphragm Q is much more convenient than the cylinder 
diaphragms as the opening can be made gradually larger or smaller by 
simply turning a small lever back or forth. 



8 Elements of Vegetable Microscopy. 

If a greater concentration of light is desired than is produced by 
the concave mirror O, a condenser is used, which is placed in position 
beneath the stage. The best form is the Abbe, type, [figure 28.), consist- 
ing of one lens or a system of lenses for converging a large beam of 
light. The condenser is used for great magnification and is invaluable 
in studying stained specimens which are to be differentiated by color 
rather than by outline. 

Illumination : — No fixed rule can be laid down in regard to the size 
of opening in the diaphragm to be used for any given magnification, 
as the amount of light to be passed through a specimen depends some- 
what on its nature and thickness. As a general rule, large diaphragms 
are used for low powers with weaker illumination and small ones for 
high powers with strong illumination. Weak illumination is brought 
about by the plane mirror, stronger by the concave mirror and the use 
of a condenser if desirable. Actual laboratory practice is better than 
many words in teaching the student what is the best illumination of 
an object. 

Optical parts : — The objectives are the most important parts of the 
whole microscope. Instead of one lens, they consist of a system of two, 
three or four lenses, some of which are simple, others compounded of a 
convex crown lens and a concave flint lens as described on page 11 
under chromatic aberration. The front lens of the system always has a 
plane face which is turned towards the object, and is usually a simple 
lens (plano-convex). Such a system of lenses is almost free from 
aberration defects. 

Figure 2Q represents an objective composed of three lenses, one 
simple one, and two compound ones. The shaded lenses are flint glass. 
Objectives are designated usually by numbers which are the focal 
lengths. Sometimes they are lettered, as A, B, C, etc. If an objective 
is marked, say 1 inch or 2 A inch, this means that its magnifying power 
is the same as a simple lens whose focal length is 1 inch or % inch. In 
order to know which is high power and which low power, the student 
should remember this rule : 

The smaller the number or fraction on the objective, the higher its 
magnifying power. The objectives mostly used in vegetable histology 
are the 1 inch, f inch and \ or \ inch. The distance between the 
front lens of the objective and the object when in focus is about the 
same as the focal length of the glass used. 

Objectives are either dry lenses or immersion lenses. If, as is 
usually the case, there is an airspace between the objective and the 
object, the lens is called a dry one ; if a liquid is between the objective 
and the object, the lens is called an immersion lens. The liquid may 
be water or an oil. If water, we have a water immersion lens, if oil, an 
oil immersion lens. If the index of refraction of the oil is about the 
same as that of glass, we have a homogeneous immersion lens. Cedar 
oil thickened by evaporation is an example of such. Lenses intended 



Elements of Vegetable Microscopy. 9 

for immersion must be constructed accordingly. The great advantage 
of immersion is that the angle of the cone of light that can be utilized 
by the lens is considerably increased, thereby increasing the illumina- 
tion and the efficiency of the microscope. 

Angular aperture of a lens : — The efficiency of an objective is in 
great part dependent upon the amount of light it can take in from the 
object to •form its image. This is approximately measured by the so- 
called angular aperture of the objective. For a single lens, this is the 
angle formed by lines joining the focus with the edges of the lens, thus 
figure 30 y A B C=angular aperture. 

In an objective it is the angle made by drawing lines from the focus 
to the edges of the uppermost lens. Thus ABC ( figure 31 .) is the 
aperture of the system of lenses. More accurately, the cone of light 
that the objective can take in is proportional to the sine of half the 
angular aperture, usually expressed sine (u). 

Eyepiece or Ocular : — The eyepiece universally used is Huyghens', 
a negative eyepiece, (see figure 32.) This consists of two plano-convex 
crown lenses, the lower one being the larger, less magnifying, (its focal 
length being three times that of the upper lens). It is known as the 
field lens. It increases the field of vision, i.e., the number of points of 
the object that are made visible through the instrument. The upper 
lens is known as the eye lens. It magnifies the image formed by the 
objective. Both lenses have their convex surfaces turned towards the 
object, (see figure 32.) Midway between them is a perforated diaphragm, 
the object of which is to cut out edge rays from the image and thus de- 
crease spherical aberration. The virtues of the Huyghens' eyepiece 
are that it corrects chromatic aberration, enlarges the field of vision, and 
forms a flat image i. e., all points of the image are in focus at the same 
time. This latter quality is essential in all good microscopes. In all 
negative eyepieces, the image of the object is formed between the two 
lenses, and is then further magnified by the eye lens. The lenses tak- 
ing part in the formation of the first image are, therefore, the objective, 
and the field lens of the eyepiece. In positive eyepieces, the first image 
is formed below the field lens, i. e., the ocular takes no part in its for- 
mation. An example of such is Ramsden's eyepiece. 

Oculars are designated by letters or numerals, and what was said 
in regard to the numbers on objectives, applies to oculars. Oculars 
most commonly used are the 2 inch, 1% inch and 1 inch. These num- 
bers are focal lengths. 

There is a particular order that should be observed in changing the 
lenses in passing from a low power to a high one. For ex., suppose 
there are two objectives 2 A and y% inch and two eyepieces, 2 and 1 inch, 
the following is the best order for changing these : 
Objective Eyepiece 

2 A inch 2 inch Low power. 

yi " 2 " Medium " 

% " r " High 



io Elements of Vegetable Microscopy. 

This means, to increase magnification, begin to change glasses at 
the objective. 

Tube Length: — Magnification may also be increased by drawing 
out the inner tube, which increases the distance between the objective 
and the plane of the image, and consequently the size of the image. 
The tube length however is usually kept constant, either 160 m. m. 
(6.3 inches) or 216 m. m. (8}4 inches.) The scale on the inner tube regu- 
lates the length. 

As the magnifying power is increased, the field of view becomes 
smaller, illumination of the image decreases, and the image is increased 
in size. 

Camera lucida : — This is a drawing apparatus which is attached to 
the ocular, and is used whenever it is desired to make accurate de- 
lineations of the object. By means of it, a white surface of paper, on 
the table along side of the instrument, is reflected into the eye while it 
receives the image, and thus a pencil point may be traced on the paper 
along the lines of the image, giving an accurate drawing. The Abbe 
camera is the best form in the market at the present time. In drawing, 
the microscope must be erect, and the paper horizontal, and at the dis- 
tance of distinct vision, about 12 inches. 

Determination of Magnifying power of a microscope : — The mag- 
nifying power for certain combinations of objectives and eyepieces and 
tube length is usually stated by the makers, so that it is hardly neces- 
sary now to determine the magnifying power. But sometimes the rating 
of the makers is not correct and we might want to use a different 
tube length and, again, the distance of most distinct vision for our eyes 
might not be the average distance, viz., 12-14 inches, in which case a 
new determination must be made. 

A Stage Micrometer \ — a piece of glass accurately ruled to hun- 
dredths of a millimeter — is placed on the stage and brought into focus. 
By means of a camera lucida, the magnified scale and an accurate m. m. 
scale, placed at the distance of distinct vision, alongside the micro- 
scope and parallel with the micrometer scale are brought into super- 
position. The number of m m. divisions covered by a definite number 
of the micrometer scale divisions is then noted. Suppose each magni- 
fied scale division covers 5 m. m. of the rule, what is the magnifying 
power? One m. m. is equal to too micrometer divisions, the 5 m. m. 
covered by one micrometer space are equal to 500 micrometer divisions. 
Hence one micrometer division has been magnified so as to cover a 
space 500 times as wide, i. e., it has been magnified 500 times. This, 
then, is the power of the instrument for the particular combination. 

Source of light .•— -The best source of light is a white cloud, or the 
diffused light reflected from a white wall or other white object. Never 
use direct sunlight. Light from the blue sky is not so good as that from 
a white surface. There is a tendency among beginners to use the strong- 
est light possible. This is injurious to the eyes and often obscures de- 
tails of the object by its dazzling glare. A window facing north is best. 



Elements of Vegetable Microscopy. i r 

Requisites of a good microscope .-—It goes without saying that the 
best workmanship must be found in the mechanical parts. The foot, 
pillar, arm, stage, etc., must be of sufficient weight and strength and 
size. 

For the optical parts, five points must be considered. 

i. Working Distance : — This is the distance between the front lens 
of the objective and the object. The lower the magnifying power, the 
larger the working distance, in general. Working distance has no fixed 
relation to the focal length, but varies with the mode of construction 
and the aperture of the objective. Of two objectives having the same 
focal length, that one with the larger working distance is to be chosen. 
As the power is increased, the working distance is decreased. It is 
often advantageous to gain working distance at the expense of magni- 
fication, as the manipulation of objects on the section slide is made 
easier. 

2. Penetrating power or focal depth : — This is the vertical range 
through which the parts of an object not precisely in the focal plane 
may be seen with sufficient distinctness to enable their relations with 
what lies exactly in that plane to be clearly traced out. It is larger, 
the smaller the magnifying power and numerical aperture are, and vice 
versa. Of two objectives having the same power, but different working 
distances, that one will have the more focal depth whose working dis- 
tance is the greater. It is often desirable to see for a considerable 
distance into an object. In such cases, low power must be used. 

3. Flatness of field : — All parts of the image must be in focus at 
the same time. 

4. Defining power : — The power to form an image in the highest 
degree, sharply defined and free from color. This quality is governed 
by the objectives only and depends on accurate centering of the lenses 
and completeness of correction for spherical and chromatic aberra- 
tions. Want of defining power is indicated by blurring of clearly- 
marked lines or edges, and by general fog. 

5. Resolving power: — By which very minute and closely approxi- 
mated markings, whether lines, striae, dots or apertures, can be sepa- 
rately discerned. This power varies directly as the aperture of the 
objective. High powers have the greatest resolving power. 

Care of the microscope : — The stand should never be wetted with 
such substances as alcohol, soap, etc., which dissolve lacquer. If it is 
necessary to clean the stand, moisten with water and dry with an old 
linen rag, rubbing with the grain of the brass. Never examine objects 
lying in acids or alkalies, or other chemicals without putting on a 
" cover " glass. If liquid happens to get on the objective, rinse off at 
once with water and dry with an old linen rag, or Japanese filter paper. 

Be careful not to force the lens down on the cover glass. Exercise 
great care in putting objectives and oculars on or off, lest they be 
dropped and injured. 



12 Elements of Vegetable Microscopy. 

Directions for using the microscope : — 

i. The instrument should be placed directly in front of the ob- 
server, with the pillar facing backward. Wipe the mirror with a soft 
rag and turn it so that a beam of light is thrown up through the dia- 
phragm. All work should be begun with the low power objective. 
The body of the microscope should be about vertical so as not to inter- 
fere with mounting in fluid media. 

2. The object mounted on a glass *' slide " in a suitable liquid and 
covered with a "cover glass", is brought to the centre of the dia- 
phragm, and focused by means of the coarse adjustment in the follow- 
ing manner. Using the left thumb and forefinger to adjust the slide, 
with the right hand the objective is brought down so that it all but 
touches the cover glass, then while looking through the eyepiece, slowly 
raise the tube by the coarse adjustment until the object is in view; 
from this point the exact focus can be made by turning the fine adjust- 
ment screw. 

3. Never lift the slide from the stage, but, having raised the objec- 
tive, especially in case of high powers, slide it off the stage without 
upward movement. 

4. Accustom yourself to use both eyes indifferently, and always 
keep both eyes open. It is preferable to observe with the left eye as it 
is more convenient in making drawings. 

5. To mount an object \ place it in the centre of a slide in a drop 01 
liquid, say water, rest a cover glass on its edge near the object in a 
slanting position and gradually lower it by means of a teasing needle 
or forceps, in order to avoid entrapping air bubbles. The cover glass 
should be previously cleaned with a soft rag or lens paper and then 
handled by the forceps only. Any superfluous water on the slide is 
taken up by a camel's hair brush or blotting paper. 

6. Cleanliness should characterize all the work of the microscop- 
ical laboratory. All apparatus, slides, cover-glasses, etc., should be 
kept scrupulously free from dirt. The glasses of the objectives and 
eye-pieces should never be touched with the fingers. Whenever they 
need cleaning, breathe upon them and wipe with a soft clean linen 
rag or a piece of "Japanese filter paper ". 

7. All objects observed should be drawn. Drawings are useful not 
only in explaining to others the structures observed, but they are 
themselves great aids also to accurate observation, and are equally 
helpful in giving vividness and permanency to knowledge. 

Each student should provide himself with a blank-page drawing 
book and a hard pencil ( Faber's HHH ). It is excellent practice to 
keep a record in writing of work done in the laboratory besides mak- 
ing drawings. 

Some accessory apparatus necessary in histological work : — 
1. Micrometer, preferably metric scale. Convenient scale is hun- 
dredths of a millimeter. 



Elements of Vegetable Microscopy. 13 

2. Section Razor, flat on one side, slightly hollow on the other, 
for making thin "sections" or slices of bodies ; also a hone and a strop. 

3. A graduated ruler, having both English and metric scale. 

4. Dissecting needles. 

5. Sharp-pointed scissors preferably bent. 

6. Delicate forceps or pincettes. 

7. Watch glasses, for holding sections. 

8. Small porcelain evaporating dish. 

9. Camel's hair brushes, assorted sizes. 

10. Glass section slides, 3'xi', not too thick, ground edges, 

n. Cover glasses, %' circles No. 2. 

12. Camera lucida for drawing. 

13. Polariscope. 

14. Draughtsman's dividers, for drawing. 

15. Microtome, for section cutting. 

16. Turn-table for ringing sections. 

17. Pipettes, glass rods, blotting paper. 

Microscopical apparatus may be obtained from any large dealer, as Bausch & Lomb 
Opt- Co., Rochester, N. Y. Queen & Co., Philadelphia. Cuts of apparatus may be seen in 
catalogues or in larger works on Microscopy, as Behren's Botanical Microscopy. 



VEGETABLE HISTOLOGY. 

CHAPTER II. 

In order to acquire some familiarity with the manipulation of the 
microscope before studying vegetable objects, it is well to study some 
simple things like cotton, silk, wool and linen fibres, and these are 
chosen because they sometimes occur accidently on the slide when we 
are studying other things. 

Lesson I. — Linen, Cotton, Silk, Wool. 

Linen: — Scrape a linen thread on a glass slide with a knife blade 
to a woolly mass, mount a little of this on a slide in a drop of water, 
taking care that the fibers are wetted and no air adheres to them, then 
cover with a cover glass as described above. The student should guard 
against an error that beginners are apt to fall into, viz., putting too 
much material on the slide. A very small quantity will suffice. Exam- 
ine with low power. (%' objective and 2' eyepiece). Very little will be 
made out. Some clear, smooth, tangled threads. 

Put on high power. The linen will be seen to consist of long, cylin- 
drical, smooth fibers, thickened at intervals into nodes, with a small 
canal looking like a line running lengthwise of the fibre. At intervals 
there are faint cross lines, called pore canals. {See figure 33.) Linen 
fibres are of vegetable origin, their material is cellulose, a substance 
which is one of the chief materials found in plants. Remove the cover 
glass, add a drop of a solution of iodine in potas. iodide, then a drop of 



14 Elements of Vegetable Microscopy. 

moderately strong sulphuric acid, replace cover glass and examine 
again. The fibres are stained a deep blue color and swollen. This is 
a characteristic test for cellulose material. Iodine alone does not color 
it, but the acid acts on it, converting it into a starch-like body, called 
a myloid which stains just like starch itself with iodine. Cellulose and 
starch belong to the same group of chemical compounds, known as 
carbohydrates. 

Cotton: — Mount a little raw cotton in water. Low power — narrow, 
clear fibres, not very different in appearance from linen fibres. High 
power — Long flat bands which have caved in, often twisted like a cork" 
screw, at times striated diagonally, will be seen. The fibres do not pos- 
sess pore canals. They are the long hairs on the seeds of the cotton 
plant, the hairs being plant cells, consisting at maturity only of cellu- 
lose walls which fall together giving the fibres the appearance of a flat 
band. The filaments are about 2 cm. (* inch) long in short staple to 
4 cm. (1 f inch) long in long staple cotton, and about .02 m.m. (.0008 
inch) broad. There is a central canal running through each fibre, much 
larger than in linen fibres. The fibres respond to test for cellulose as in 
case of linen. {See figure 33.) 

Silk : — Scrape some threads as in case of linen, and mount in water. 
With both low and high powers the fibres appear about the same — shin- 
ing, dense, cylindrical, structureless, without central canal, easily dis- 
tinguished from all other spun fibres. Silk is animal in origin and does 
not give cellulose reaction. {See figure 33.) 

Wool: — This is also of animal origin. Mount some fibres from 
white woolen yarn in water. With low power the fibres are clear, 
slightly roughened on the surfaces with faint cross lines. Under high 
power, the fibres are cylindrical, containing a central axial substance 
called the medulla (not present in all hairs or wool.) The surface is 
covered by imbricated scales, like tiles on a roof, giving to the edges 
of the fibres a barbed appearance. Compare a human hair with wool. 
{See figure 33.) 



CHAPTER III. 
Lesson II— Yeast (Torula or Saccharomyces Cerevisi^e.) 

This is a plant and is that which causes alcoholic fermentation in 
sugar solutions. It is a plant of the simplest kind, consisting of a sin- 
gle cell. Plants are divided into four series according to their com- 
plexity of structure and functions. 

Thallophyta — (Thallus plants) \ 

Bryophyta — (Moss plants) >• Cryptogamia or Flowerless plants. 

Pteridophyta — (Fern plants) ) 

Spermaphyta or Phanerogamia or Flowering plants. 

The thallophyta are a large group of plants in which there is no 
clear differentiation of the plant body into root, stem and leaf. A vast 



Elements of Vegetable Microscopy. 15 

number of forms are included, which differ greatly among themselves 
in complexity, but even the highest forms never have true roots, and in 
the great majority of cases, there is no differentiation into stem and 
leaves. There is never a clear differentiation into epidermal, funda. 
mental and fibro-vascular systems of tissues as in the ferns and flower- 
ing plants. 

The thallophyta are divided into a number of groups, two of which 
are the Schizophyta or fission-plants, and Fungi or moulds, to the latter 
of which the yeast plant belongs. Yeast is a degenerate form of fungus. 
It consists of rounded or ellipsoidal cells which occur either singly or 
loosely united into short chains. The diameter of the cells varies from 
2700 to two " ln ch (average 30V0 inch.) 

Each torula is a thin-walled sac or bag containing a semi-fluid mat- 
ter, in the center of which there is often a space full of a more clear 
and watery fluid than the rest, which is termed a vacuole. The sac is 
comparatively tough, but may be easily burst and the contents thrown 
out. The whole structure is called a cell, the sac being the cell-wall and 
the more solid portion of the contents, the protoplasm. 

Torulae break down sugar mainly into alcohol and carbon dioxide 
gas, and at the same time increase in number. Multiplication takes 
place in this way. A small protruberance begins to form on the parent 
torula, which grows larger, forming a bud. The bud increases until it 
attains the size of the parent torula and eventually becomes detached, 
though generally not until it has developed other buds on itself and these 
still others. The torulae produced thus by gemmation or budding, are 
apt to adhere to each other for a long time and thus produce heaps and 
strings. {See figure 34.) 

Sow some fresh baker's yeast in Pasteur's fluid and keep in a warm 
place. As soon as the solution begins to froth and the yeast is mani- 
festly increasing in quantity, it is ready for study. Fermentation is 
most active between 28 and 34°C. At 38°C growth ceases. 

Mount a drop of the liquid and examine with low power, minute 
specks will be seen. 

High power. — Note the homogeneous transparent cell-wall ; the 
less transparent protoplasm, often containing a few clear shining dots ; 
vacuole, sometimes absent. Place a drop of fuchsine solution at edge 
of cover-glass, (help it to run in by placing a piece of blotting paper at 
other side of glass.) Note what cells stain soonest and most deeply. 
The cell-wall is unaffected ; protoplasm is stained reddish. Vacuole 
is unstained, though frequently it appears pinkish, being seen through 
a colored layer of protoplasm. 

Make a new mount and apply iodine solution. The protoplasm 
stains yellowish brown, cell-wall is unstained. Note the absence of any 
blue coloration ; starch therefore is not present. 

The yellowish-brown color of protoplasm with iodine sol. is one of 
the tests for protoplasm. 



1 6 Elements of Vegetable Microscopy. 

Torula is classed among the plants because it has i, a cellulose 
cell-wall, 2, the power of constructing protoplasm (living matter) out of 
comparatively simply substances such as ammonium tartrate which is 
distinctively a vegetable peculiarity. But though a plant, it contains 
neither starch nor chlorophyll, and cannot obtain the whole of its food 
from inorganic compounds, thus differing widely from green plants. 

Pasteur's Solution :-Potas. phosphate 2pts.; calc. phosph. i\ 
pts ; mag. phosph. 2 pts.; ammonium tart. 10 pts.; cane sugar 150 \ 
pts.; water 837.6 pts. 



CHAPTER IV. 
Lesson III.— Bacteria, (Schizomycetes or Fission Mould.) 

One of the subdivisions of the thallophyta series of plants, as was 
noted in Lesson II, is the schizophyta. This class is composed chiefly 
of the schizomycetes or bacteria. These are extremely low forms of 
plant life, being exceedingly simple in structure and always minute, 
some of them being the smallest of known organisms. They are mostly 
unicellular or if consisting of cell-aggregates, as is sometimes the case, 
the cells are united in a simple way, and have very little dependence 
upon each other. They are the most abundant of organisms, the 
largest being not more than T q^oo inch in diameter and the smallest not 
more than T x o of that. All are chlorophylless, i. e., without coloring 
matter. The cells agree in having mostly rigid transparent walls and 
colorless cell-contents, but different species differ considerably in form, 
size, etc. Their usual mode of increase is by fission or splitting, but 
they also produce very minute so-called spores, by a method known as 
internal cell-formation. (See later.) 

In some species the cells, after fission, immediately become inde- 
pendent ; in others they remain united for a time to form filaments or 
chains of various lengths. Many of the species in some stage of their 
development have the habit of secreting a jelly and increasing rapidly 
by fission, forming large gelatinous colonies. These are called 
zodglcea-masses . " Mother of vinegar " and the so-called "blood-rain," 
consisting of red gelatinous spots often found on putrefying bread, are 
examples of zooglcea-masses. 

In all putrefying fluids or solutions that contain decaying organic 
matter, bacteria swarm in myriads. They are in fact the inciting cause 
of putrefaction. By their agency also milk sours, wine is converted 
into vinegar etc. So far as animal life is concerned, some of the species 
are harmless, or perhaps even beneficial, while others are the source of 
some of the most dreaded and most fatal of diseases. Chicken cholera, 
splenic fever, small pox, diphtheria and leprosy are examples. A 
peculiar interest therefore attaches to the study of these organisms. 



Elemeiits of Vegetable Microscopy. 



17 



Bacteria are killed at about 6o°C. (i4o°F.) but the spores can, in 
many cases, resist a temp, above ioo°C. Spores are little, specialized 
cells, corresponding to the ovules of flowering plants, which have the 
power and function of reproducing a new plant just like the original. 

Bacteria are conveniently grouped according to their forms. These 
are (a) the micrococcus or spherical form, (b) the bacterium or rod-like 
form, (c) the bacillus or filiform form, and (d) the spirillum or coiled 
form . See figure 33. 

Infuse some hay in warm water % hr., filter and set aside 36 hrs. 
or more. The liquid becomes cloudy and swarms with bacteria. 

Examine a drop under high power at once, focusing very care- 
fully. Note the moving bacteria, elliptic or rod-like, sometimes form- 
ing short jointed rows. The cells have an outer, more transparent 
layer enveloping a more opaque matter. 

Apply drop Iodine Sol. — The bacteria are killed, motion forward 
ceases, the cells are stained and become more conspicuous. The en- 
velope does not stain. 

The hay-infusion after a time developes a scum or zooglcea. 

Resting-bacteria or Zooglcea stage : — Mount a little of the scum and 
note with high power. Myriads of bacteria resting in a gelatinous mass 
will be seen. Although they do not move away from their places, the 
bacteria will be seen to have a wiggling or oscillatory motion, known 
as the Brownian movement. This motion is not a vita one but is char- 
acteristic of very small bodies, whether dead or alive. Fine clay, pum- 
ice, lamp-black, gamboge show the same motion. The cause is not 
definitely known. 

Treat scum with Iodine Sol. — The bacteria stain, the gelatinous 
material does not. Other forms that may be found in the infusion are 
micrococcus, bacillus, spirillum. 

In order to show the position of the plants already studied, as well 
as those to follow, in the system of classification of plants, a table of 
the thallophyta, with the subdivisions, is here appended. 



Classes. 

1. Myxomycetes. 

2. Schizophyta. 



3. Algae. 



Thallophyta Series. 
Sub-classes. Orders. 



Ii. Schizomycetes. 

(Bacteria.) 
\2. Cyanophyceae. 
1. Diatomaceae. 



Genera. 



2. Chlorophyceae. 



2. 

3- 

4- 

5. Conjugatae. 

6. 



2 Spirogyras 

3 Zygnemas. 

4 



i8 



Elements of Vegetable Microscopy. 



4. Fungi. 



3. Phycomycetes. 



4. Ascomycetes. 



1. Zygomycetes (Mucor Mould.) 
2. 

3- 

1. 

2. Erysiphese(Penicillium 

3. Mould.) 

4. Pyrenomycetes (Ergot of rye.) 

5- 

6. Saccharomycetes (Yeast.) 



g. Basidiomycetes. 2. 

3. Hymenomycetes 



1 
2 
3 
4 
5Agaricineae 

(Mushrooms.) 



5. Lichenes. | 

The table is incomplete, only those sub-divisions being given with 
which the plants studied in these lessons are concerned. 




Elements of l^egetable Microscopy. 19 

CHAPTER V. 

Lesson IV.— Spirogvra. 

This belongs to the 3rd class of the thallophyta series of plants, 
known as Algce. This class includes nearly all the thallophyta which 
contain chlorophyll (leaf-green). 

The algae are an assemblage of quite simple plants, none of the 
members attaining any great degree of complexity. For the most part 
the plant body consists of an elongated filament composed of united 
cells ; sometimes however they form surfaces and in other cases the 
plants are unicellular, or aggregated into communities. In these 
plants we find the first examples of undoubted sexuality and throughout 
the group, the organs and methods of fertilization are nearly enough 
uniform to enable us to use them as distinguishing characters. 

The algae are aquatic plants and inhabit either fresh or salt water. 
They abound in ponds and slow running streams. 

Spirogvra will illustrate the characteristics of the class. Its posi- 
tion in the system of plants is given in the table p. 17. It belongs to 
the order, Conjugatae. This order differs from all other algae in the 
peculiarly complex structure of the chlorophyll bodies and the mode 
of sexual reproduction (except some of the diatomaceae) which consists 
in the direct conjugation or union of two ordinary vegetative cells; 
hence the name conjugates. Spirogyra is a filamentous plant, very 
common in ponds and ditches as a green scum composed of silky, 
green, threads which sometimes attain a length of six or eight inches. 
The filaments are unbranched and composed of a row of cylindrical 
cells, all alike and independent of each other, and loosely joined 
together. The name is given in allusion to the fact that the chlorophyll- 
bodies, i. e., the bodies bearing the green coloring matter, form spiral 
bands winding around the cell on the interior of the cell-wall. Some- 
times the bands are single, at other times, double or treble (Zygnemas 
have stellate chlorophyll bodies, two in each cell, arranged axially). At 
intervals along each band, are to be seen highly refractive lenticular 
bodies called pyrenoids. When exposed to the light for some time, the 
pyrenoids would be found, on appropriate treatment, to be surrounded 
by starch grains. 

The cells are bounded by well marked, refractive, cellulose walls. 
Next to the wall is a thin layer of protoplasm better seen by staining 
with iodine sol. The chlorophyll bands are in contact with this layet 
of protoplasm. The greater part of the interior of the cell is occupied 
by a large vacuole, containing cell-sap, i.e., water with substances in 
solution. Each cell has a usually centrally placed, distinct, protoplasm- 
ic body, known as a nucleus, with radiating extensions of protoplasm 
passing from it to the outer layer of protoplasm next the cell-wall. 
The growth of spirogyra in length is brought about by cell division. 



20 Elements of Vegetable Microscopy. 

Each cell is repeatedly divided into two equal parts by the appearance 
in it of a cross partition. This process takes place during the night 
and special precaution must be taken in order to study it. This method 
of cell formation is the general mode throughout the vegetable king- 
dom. {See figure 36.) 

The method of reproduction in spirogyra is a sexual one and known 
as conjugation. This process occurs from early spring to June and 
July, but can be induced when the plant is under cultivation by allowing 
the water in which it is growing to slowly evaporate. Two filaments 
arrange themselves side by side, and the cells lying opposite each 
other send out each a process or tube ; these unite and the protoplasm 
from one cell passes over and coalesces with that in the cell opposite. 

The result of the process is a new cell called a zygospore. This is 
set free by the decay of walls of the old cell and falls to the bottom of 
the water and rests until proper time for growth. 

There are a number of species of spirogyra. Mount some filaments 
in water and examine with low power. 

Note: — The great length; uniform diameter; cell contents, color- 
less, except the conspicuous green bands. 

High power. Note shape of cells ; relative length and breadth ; cell 
walls ; chlorophyll bands, spirally arranged, with crenulated and 
wrinkled margin, and nodules at intervals along them (pyrenoids). 
Search for a nucleus. Apply iodine and note results. {See figure 37.) 



CHAPTER VI. 

Reproduction. 

This is the power that plants possess of giving rise to new individ- 
uals and the process takes place by one of three ways, viz., Division, 
Rejuvenescence, and Union. The first two modes are asexual, the last 
sexual. 

There are three varieties of reproduction by division : 
f Fission. 
Division.^ Gemmation. 

[internal cell formation. 
Fission : — The most common mode of division. This is the separa- 
tion of a cell into equal portions. 

a. A constriction takes place in the middle of the cell and along 
the plane of this constriction, the cell walls may grow inward until the 
cell contents become separated into two equal portions. This mode 
has been observed in some of the lower algcz, (spirogyra). {See fig- 
ure 38.) 

b. A delicate partition of cellulose may at once be formed through 
the middle of the cell. This is the usual mode by which " tissues " are 
formed and growth takes place in all the higher plants. {Figure 39.) 



Eleme?its of Vegetable Microscopy. 21 

Gemmation .-—This method is found only in the yeast plant and its 
relations. (See Torula for description.) 

Internal cell formation:— -The protoplasm of a cell breaks up into 
two or more rounded masses, each of which eventually acquires a cell- 
wall of its own, and escapes from the parent cell by the rupture or decay 
of the old cell-wall. Example, ascospores in lichens and some fungi, 
and pollen grains in the anthers of flowering plants. 

.Rejuve?iescence : — The protoplasm aggregates into a rounded mass, 
escapes through the cell-wall, and subsequently forms a new cell-wall. 
Commonly before the new cell-wall forms, the protoplasm forms cilia 
and moves about. Rejuvenescence is found only among lower forms 
of plant life, for ex., cedogonium, one of the algae. 

As was said above, Division and Rejuvenescence constitute asexual 
reproduction. There are two modes of asexual reproduction. 
j 1. Vegetative reproduction. 
( 2. Spore " 

In the former, the parent plant throws off from itself ordinary vege- 
tative cells ; in the latter, specialized cells called spores are formed. 
Examples of the first are bacteria, cell multiplication in higher plants, 
multiplication in case of many plants by bulbs, tubers, stolons, offsets, 
etc. 

Spore-reproduction by the asexual process is exemplified in many 
flowerless plants. Examples, spores on the gills of the common mush- 
room, motile spores so commonly produced by the mosses and ferns. 
Spores are commonly borne in a special organ called a sporangium. 

Sexual Reproduction. — Union of Cells. 

This consists in the coming together and blending of the protoplasm 
of two distinct cells to form a new one. 

a. The uniting cells may be alike and the process is then known as 
conjugation, and is found only in certain low forms of plant life, as, 
mucor (a mould,) diatoms, spirogyra, desmids, all of which belong to 
algae. 

b. The uniting cells may be unlike, the process being then known 
as fertilization. One cell (the male or sperm cell) is commonly not 
only smaller but more active than the other, (called the female or germ 
cell.) Example, all higher plants. 

CHAPTER VII. 

Lesson V. Moulds. (Fungi.) 

Moulds belong to the group of plants known as fungi, which latter, 
as we have already seen, form one of the divisions of the thallophyta. 
The fungi are in their habits chlorophylless saprophytes, or parasites. 
(A saprophyte is a plant which derives its sustenance from decaying 
organic matter. A parasite lives on other organisms.) In all but 
a few instances, (see torula), their vegetative parts consist of slender 



22 Elements of Vegetable Microscopy. 

segmented or unsegmented, usually colorless filaments, each one being 
known as a hypha. These ramify among decaying organic debris, or 
nvade the tissues of living organisms, plant or animal, and derive their 
sustenance from them. In the simpler hyphal forms, the hyphae occur 
singly, or more or less interwoven into a tangled felt-work, but they 
are not gathered into definite forms and have little or no dependence 
on each other. In the higher groups, however, there is more or less 
division of labor among the hyphae and they become consolidated into 
false tissues which acquire definite shapes according to the species. 
Of this character are the fructifying organs, or "carpophores ," which 
constitute the above ground parts of the agarics, puff-balls, cup-fungi 
etc., and the sclerotium, a compact hard mass of thick-walled hyphae, 
which serves as a resting stage in the development of some species, for 
example, ergot of rye. 

Fungi reproduce asexually by means of spores known as gonidia or 
conidia. These are, as a rule, thick-walled cells, which become sepa- 
rated from the parent hyphae in ways which are more or less charac- 
teristic in the different groups. In all hyphal fungi, the hyphae consist 
of two portions ; the vegetative which ramifies in the substratum, often 
forming tangled felt-like masses of threads, called the mycelium ; and 
the reproductive, which comes to the surface. The latter produces the 
conidia, which may be borne on isolated filaments, as in the bread- 
mould (penicillium), or on a carpophore, which produces a spore-bearing 
hymenium. The common mushroom (agaricus campestris) is an exam- 
ple of the latter, the plate-like bodies or gills on the under surface of 
the cap constituting the hymenium. 

In a large number of fungi, including some of the most highly orga- 
nized forms, sexual reproduction is unknown. In other species, sexual 
reproduction takes place and this may be by several methods, viz., 
conjugation and formation of so-called oospores. 

Penicillium Glaucum (Bread Mould). 

(For position of this plant in the system, see scheme page 18.) This 
mould is familiar to everyone from its forming sage-green crusts upon 
bread, jam, old boots, etc. It may be obtained at any time by placing 
a moist piece of bread under a bell-jar in a moderately warm place. 
When spores appear, sow some in Pasteur's fluid (see under torula). 
Moulds growing in this fluid are easier to examine than when growing 
on bread. On examining a patch of mould on the surface of the fluid, 
it is found to consist of a horizontal felt work of delicate tubular fila- 
ments, the hyphae, forming a crust like so much blotting paper, which 
is known as the mycelium,. Hyphae project from this into the air and 
bear a green powder, the spores. These hyphae are called aerial. From 
the mycelium, other hyphae grow down into the liquid and are called 
submerged hyphae, corresponding somewhat to the roots of higher 
plants {see figure 40.) Carefully make a thin section of the mycelium 
by cutting between two pieces of cork and note with low power. Then 



Elements of Vegetable Microscopy. 23 

with high power, note, — Each hypha has a transparent wall and proto- 
plasmic contents and is divided by transverse partitions into a number 
of cells. Each cell has several large clear spaces, the vacuoles and a 
number of nuclei which, however, are only visible by staining properly. 

The hyphae frequently branch and are inextricably entangled with 
one another, but every hypha with its branches is quite distinct from 
every other one. 

Note the aerial hyphae, with brushes of branches, which become 
constricted on their ends into a series of rounded spores, like a row of 
beads. These hyphae which bear the spores, or conidia, are called 
conidiaphores. The conidia form the loose green powder characteristic 
of the mould. The spore is a round transparent sac, enclosing a mass 
of protoplasm and is in all essential respects similar to a torula. When 
sown in an appropriate medium (Pasteur's solution) it germinates, and 
forms hyphae from several points, forming a new plant like the origi- 
nal one. {See figure 40.) 

Note the submerged hyphae. Stain different specimens with fuch- 
sine, haematoxylin and iodine (see staining reagents) and note the 
results. 

Mucor Stolonifer. 

This is another mould belonging to the fungi, for the position of 
which in the system of plants, see scheme page 18. It may be grown 
by keeping some bread very moist and warm under a bell-jar, or by 
placing some moist poke-root in a bottle and closing. Mucor is very 
similar to penicillium in its growth, consisting of a mycelium from 
which grow erect or aerial hyphae, each one bearing a rounded, dark 
head, or spore case, looking like a pin head and called a sporangium. 
The wall of the spore case is beset with minute asperities of oxalate of 
lime and inside the case are a great number of minute oval bodies, the 
spores, held together by a transparent intermediate substance. When 
ripe, the thin and brittle coat of the case bursts at the slightest pressure, 
setting free the spores. A little portion of the wall of the spore-case 
remains adhering to the stalk as a collar. The cavity of the stalk 
does not communicate with the sporangium but is cut on by a bulging 
partition, forming a central projection known as the columella. {See 
figure 41.) 

The spores are oval, and larger than those of penicillium, consist- 
ing of a sac enclosing protoplasm and a nucleus. When sown in a 
proper medium, they send out hyphae and produce a new plant. The 
spores are at first colorless, but when ripe are colored and give the 
black appearance to the sporangia. 

The hyphae are cylindrical threads, longer and larger in diameter 
than in penicillium, and have no dividing partitions, so that each 
hypha however long, with all its branches, forms a single cell. The 
hyphae contain protoplasm interspersed with numerous vacuoles and 
nuclei. ( See figure 41.) 



24 Elements of Vegetable Microscopy. 

Examine mucor in water on a slide with low and high powers. Note, 
hyphae, sporangia, columella, broken spore-cases, spores, vacuoles 
etc. Also use fuchsine, and iodine stains and note results. Draw, pay- 
ing attention to relative sizes of the parts. 

Ergot of Rye. (Claviceps Purpurea) 

Ergot is a fungus formed of hyphae. These interpenetrate the rye 
grain, and finally consume it entirely. At one stage of the develop- 
ment, the fungus forms a dense mass of thick, hard, dark purple hyphae, 
known as the sclerotium, which is the Ergot grain. This is a resting 
stage, the grain lying dormant until spring, when, if placed in warm 
damp soil, there arises a number of stalked bodies with globular heads, 
in which the spores are produced. 



CHAPTER VIII. 
The Tissues of the Higher Plants. 

The lessons thus far have been given to the study of some of the 
simple plants, for the purpose of giving an idea of the nature of the 
lowest forms of plant life as well as familiarizing the student with the 
use of the microscope and the manipulation of objects on the slide. 
Some of the plants studied play an important role in the life economy, 
for ex., yeast, bacteria, moulds, and thus deserve close study. While 
studying these plants, we have learned what is meant by a plant cell, 
and the subsequent lessons will be devoted to a study of the various 
kinds of cells, and webs of cells, known as ''tissues", found in the 
most highly developed and complex plants, the phanerogamia, or 
flowering plants. 

The peculiarity of these is that there is a great division of labor, with 
corresponding tissues and organs, which have been differentiated from 
a fundamental tissue. Thus we have the leaf, an organ for manufac- 
turing protoplasm and starch ; the flower, which is the reproductive 
organ ; the stem, the channel for conveying sap ; the roots for imbibing 
water and nourishment. The cells are differentiated into distinct tissues. 
On passing down to the lower series of plants, these tissues become 
simpler until, finally, in the thallophyta and most of the bryophyta, we 
have no distinction of tissues at all. Those plants consist of a homoge- 
neous mass of cells, as we have seen in the case of algae and moulds. 

The various tissues, or cell-webs, of the flowering plants, viz., epi- 
dermal, ground, fibro-vascular, stony, etc., tissue are all derived from 
cells that were at one time all alike. By various physical and chemical 
modifications, the cells come to differ from one another aud thus to 
give rise to the different tissues. The cells of stony tissue, as found 
in shells of nuts, were once like the soft cells of a leaf, but they became 
subsequently hardened and modified. 



Elements of Vegetable Microscopy. 25 

A celt has been defined as a nucleated mass of protoplasm. It may 
or may not possess a cell-wall of different composition. In the major- 
ity of vegetable cells such a wall is present, while most animal cells 
are destitute of it ; but in all essential respects animal and vegetable 
cells resemble each other. Cells are the structural units of the organ- 
ism. All plant bodies are composed of cells, or of these together with 
the products of cell activity. Within the compass of the cell occur all 
those essential phenomena which are called vital; the life of a plant 
resides in its cells ; the sum of the activities it exhibits is the sum of 
the activities of its component cells. 

Vegetable cells are on the average not more than the one five hun- 
dredth or one six hundredth of an inch in diameter, though in some 
cases they are large enough to be distinctly seen by the unaided eye, 
as in the flesh of the Watermelon and the pith of Elder; in rare in- 
stances, as the internodal cells of Chara, they may even be more than 
an inch long. Some cells on the other hand, are so small as to be 
barely visible under the highest powers of the microscope. Ex., bac- 
teria. 

The primary form of cells appears to be that of a sphere or sphe- 
roid, but commonly, especially in the tissues of the higher plants, they 
acquire forms quite different from this, and even within the limits of 
the same organism, the shapes may be exceedingly various. This may 
be due to mutual pressure, to unequal growth caused by the unequal 
operation of various physical forces, as gravitation, light, etc., or to 
other influence. Cells, like the organs of which they are components, 
undergo many modifications of form and structure, adapting them to 
different uses. The cells which make up the body of a plant are com- 
parable to the human units which make up society. A plant is a com- 
munity or republic of cells, and to understand it, one must understand 
the individuals that compose it. 

Lesson VI. — Typical Vegetable Cell. 

As all the different kinds of cells that go to make up the various 
tissues of a plant are derived from cells that are at one time all alike> 
we will begin by a consideration of these primitive or typical cells, 
and afterwards study the various modifications. 

Peel off the skin or epidermis from the convex surface of an onion 
scale, by making a cross incision and catching the skin between the 
thumb and the knife or razor edge. Be careful not to draw along with 
the epidermis any of the thick underlying flesh of the scale. Mount a 
piece of the skin about a quarter inch square in water on a slide, cover 
carefully with a glass so as not to include any air bubbles. 

Examine with low power. Very little will be made out. There is 
a fine and somewhat irregular network. This is due to an aggregation 
in a single layer, of a number of cells, the network of lines being the 
bounding cell-walls, which are'so nearly transparent as to be almost 



26 Elements of Vegetable Microscopy. 

invisible. Inside of each cell, there is visible a small body, the nu- 
cleus, and perhaps some faintly granular matter. The cells are filled 
with a semi-liquid matter which, however, is too transparent to be seen. 

To bring out the parts better, add iodine solution and examine with 
high power. 

The cell-walls, scarcely stained, are distinctly visible. In mature 
cells aggregated to form tissues, the common cell-wall between two 
cells is made up of two like portions separated by a layer of a slightly 
different chemical substance, which is more soluble in reagents than 
the rest of the wall and shows different reactions with test reagents, and 
is known as the middle lamella. Next to the cell-wall is a layer of pro- 
toplasm, granular and deeply stained yellowish brown, called the prim- 
ordial utricle. Somewhere within the cell will be seen a dense body, 
the nucleus, surrounded by protoplasm and connected by strings of 
protoplasm with the utricle. Between the strings are vacuoles, clear 
spaces filled with cell-sap. The nucleus contains several smaller bod- 
ies, which are little nuclei or nucleoli (plural of nucleolus), {See figure 
42.) 

Remove the cover glass and add a drop of sulphuric acid. 

Place cover-glass on again and note result. The cell walls are 
found to be stained a deep blue, proving that they are cellulose in na- 
ture. Between the walls is seen a light yellow line not stained blue 
and hence different in composition from the rest of the wall. This is 
the middle lamella which is composed chiefly of insoluble pectates. 

The typical cell just described is somewhat advanced from the 
earliest stage of a cell, known as the primary meristem cell. In such 
very young cells the wall is exceedingly thin and apparently homoge- 
neous, the vacuoles are absent and the entire area enclosed by the wall 
appears to be filled with protoplasm {see figure 42.) As the cell grows 
older, its wall becomes thicker and differentiated as described above. 
By the expansion of the wall, the cavity of the cell increases faster than 
the contained protoplasm, the latter imbibes more water than it is 
capable of holding in solution and thus sap-cavities, or vacuoles are 
formed which at the maturity of the cell, often occupy more space than 
the protoplasm itself. Finally, when the cell is quite old, its living 
contents disappear altogether, and the cell is dead matter. 

As the cells develop to form the various tissues, a number of sub- 
stances make their appearance in the contents. Some of these are 
chlorophyll bodies, aleurone grains, starch, fatty oils and fats, calcium 
salts, glucosides, alkaloids, sugar, bitter principles, tannin, resins, 
gums, inulin, etc. Some of these will be studied in later lessons. 



Elements of Vegetable Microscopy. 27 

CHAPTER IX. 
Staining Fluids Giving Permanent Stains. 

Kleinenberg" s Hematoxylin : — Saturate some 70 per cent alcohol 
with calcium chloride ; let the mixture stand 12-24 hrs. over alum, 
shaking occasionally; add 8pts. 70 per cent alcohol; filter and then 
add a saturated sol. of hcematoxylin in abs. alcohol until a purple-blue 
color is produced ; let stand in a corked bottle in sunlight for a month ; 
it is then ready for use. The liquid is to be diluted as required with 
dilute alum solution. Over-stained sections are brought back to proper 
degree of staining by washing in acidified 70 per cent alcohol. (4-6 
drops hydrochloric acid to 100 c.c. alcohol). Since acids are incom- 
patible with the stain, it is best to wash the section next in alcohol or 
water containing a trace of ammonia, before making the final mount. 

Hematoxylin is an excellent nuctear and cellulose stain. It scarcely 
stains lignified material. Alcoholic sections should first be washed well 
in water and also thoroughly washed after staining. 

Beetle's Carmine : — .6 gram carmine is dissolved in 2 c.c. boiling sol. 
of ammonia ; let stand 1-2 hrs. to cool and to allow excess of ammonia 
to escape; add 60 c.c. distilled water, 60 grams glycerin and 15 grams 
absolute alcohol. Let stand for sometime and then filter. -Over-stained 
sections are washed in acidified 70 per cent alcohol, then in alcohol 
free from acid. Carmine readily stains protoplasm and nuclei. 

Fuchsine : — Dissolve .1 gram fuchsine in r6o c.c. water; add 1 c.c. 
abs. alcohol. Keep in a well-closed bottle. This dye stains lignified 
and cutinized tissues but is easily washed out of cellulose walls. 

3fethyl-gree?i : — Dissolve the dye in water to deep green color. 
This stains lignified and cutinized tissues more rapidly than cellulose 
tissue. It also stains protoplasm and the nucleus 

Safranin : — Equal pts. by volume of aniline-water (a sat. sol. of ani- 
line in water) and concentrated sol. of safranin in alcohol. Sections 
stained in this and then washed with acidified 70 per cent alcohol have 
only lignified and cutinized tissues stained. 

Gentian- Violet :— 3 pts. by wt. aniline, 1 pt. gentian-violet, 15 pts. 
alcohol, 100 pts. water. It stains lignified and cutinized tissues. 

Iodine-green : — A deep green water solution is used. It acts like 
methyl-green. It is much employed along with carmine, fuchsine or 
eosin for double staining of tissues. The stains are better used succes- 
sively than mixed together. 

Eosin:— Oil of Cloves solution is used for clearing and at same 
time staining sections that have previously been treated with gentian- 
violet or iodine-green or methyl-green. The violet or green goes to the 
lignified and cutinized tissues, while the cellulose walls are stained red 
by the eosin. 

Picric-nigrosin Sol : — Add enough strong aqueous sol. nigrosin to 
sat. sol. picric acid in water to produce a deep olive-green color. 



28 Elements of Vegetable Microscopy. 

This is a good nuclear stain. It is a good double stain, the nigrosin 
going to the cellulose and the picric acid to the lignified tissues. A 
comparatively long time is required for staining. 

Staining Fluids for Temporary Stains. 

Potassium-iodide Iodine. — i pt. iodine, 4 pts. potas. iodide, 195 pts. 
distilled water. One of most useful solutions in vegetable histology. 
Stains starch blue, protoplasm and proteids yellowish-brown, lignified 
cell-walls deep brown ; together with sulphuric acid, stains cellulose 
blue. 

Chloriodide-of-Zinc Iodine. {Schulze Sol.)— Dissolve some zinc in 
hydrochloric acid ; permit the sol. to evaporate, in contact with metallic 
zinc, until a syrupy state is reached ; saturate the syrup with potas. io- 
dide and add enough iodine to make a dark sherry-colored solution. 
May be used either on fresh or alcoholic material. Should be used in 
concentrated form. It stains cellulose blue, or violet, lignified walls 
yellow, corky walls yellow to brown, protoplasm brown, starch swells 
and stains blue. 

Phloroglucin .-—This is used in connection with hydrochloric acid 
as a test reagent for lignified tissues. Dissolve some of the substance 
in alcohol antl gradually add strong hydrochloric acid till precipitation 
begins. It is then ready for use. 

Aniline Chloride: — A 5 per cent alcoholic sol. is employed in the 
same way as phloroglucin, with hydrochloric acid, as a test for lignified 
tissues. It stains them a deep yellow. 

Cyanin Solution : — A sol. of cyanin in equal pts. of alcohol and 
water is used for testing for fats which are colored a beautiful blue after 
% hr. soaking. Glycerin may be used for washing out the superfluous 
stain. 

Alcannin Solution : — Prepared by adding to a strong sol. in abs. al- 
cohol, water until a precipitate begins to be formed and then filtering. 
It is a test for fats, resins, and volatile oils, which are colored a deep 
red. Cutinized and suberized tissues are also stained red, though not 
so deeply. 

Ammonio-ferric Alum .-—A sat. water solution is used as a test for 
tannic matters, which produce a bluish-black or greenish-black preci- 
pitate. It should be remembered, however, that occasionally other 
substances, usually related to the tannins, may be present, which are 
capable of forming dark-colored precipitates with ferric salts. 

Potas. Bichromate : — Used like ferric salts as a test for tannins, 
giving yellowish-brown precipitates. This, likewise is not an absolute 
test for tannins. 

Fixing and Hardening Reagents. 

Alcohol : — This is universally used for hardening plant tissues. It 
hardens by abstracting water. Strong alcohol possesses also in a high 
degree the power of fixing the protoplasmic contents of cells. Some 



Elements of Vegetable Microscopy. 29 

plant organs may be placed at once into absolute alcohol, while other, 
more tender, parts must be placed at first into weak alcohol (60 per cent), 
then into grades of increasing strength, as 70 per cent, 90 per cent, abs. 
alcohol. Tissues may be kept in alcohol for any length of time. They 
acquire the best condition for cutting, if they are placed in a mixture of 
equal volumes of water, abs. alcohol and glycerin 24 hrs. before section- 
ing. Other less frequently used solutions are, 

Chromacetic Acid : — A mixture of 1 pt. of .1 per cent acetic acid and 
1 pt. .2 per cent chromic acid. This is a fixing reagent and objects must 
remain in it from several to 24 hrs. They are then thoroughly washed 
in water and hardened in alcohol. 

Chromic Acid : — One per cent solution, used same as chromacetic 
acid. All chromic acid mixtures must be kept in the dark, as sunlight 
decomposes them. 

Osmic Acid : — One per cent solution, fixes immediately. Objects 
may rest in it from a few seconds to several hours, and are then washed 
out thoroughly in water and hardened in alcohol. 

Picric Acid : — In concentrated aqueous solution or 50 per cent al- 
coholic solution, for algae and higher plants. 

Softening Reagents. 

In some exceptional cases, objects are too hard for sectioning and 
therefore must be rendered soft before they can be studied. Such 
objects are wood, hard seeds, barks, dried drugs. In some cases, mere 
soaking for a shorter or longer time in cold or hot water will suffice to 
soften the specimen. In other cases, weak alkalis are necessary. A 
very good solutionis 2 per cent ammonia water (24-48 hrs. immersion. ) 
Very hard objects are placed in 5 per cent caustic potash solution. 

Clearing Reagents. 

To make sections more transparent so that the parts may be better 
seen, various reagents are used. Those most generally used are Oil 
of Cloves, Creosote, Carbolic Acid (liquid). These are used before 
mounting the section permanently in balsam or dammar. Other rea- 
gents that are sometimes used are, caustic potash (dilute), chloral-hy- 
drate, a mixture of creosote and turpentine (1:3) or creosote and alcohol 
(1:1). Delicate objects are gradually made clear even in glycerin. 

Starch is dissolved in dilute mineral acids, protoplasm in dil. alka- 
lis, oils and resins in alcohol, ether and alkalis. 

Alkalis, acids, alcohol, are used when it is desired to clear out the 
contents of cells so that the cell-walls alone may be studied without 
the interference of the contents. 

Ean de Javelle, {po&zs. hypochlorite) : -This solution has lately 
come into use as a clearing reagent, especially for tissues rich in pro- 
toplasmic contents. (Ex. meristem tissue). Time of action 5 — 15 min- 
utes. Sections should be washed out with dilute acetic acid to get rid 
of any carbonate of lime formed by exposure of the sol. to the air. 
Labarraque's sol. may also be used (sod. hypochlorite). 



30 Elements of Vegetable Microscopy. 

Permanent Mounting or Enclosing Media. 

Canada balsam : — This is a thick solution of the resin in benzene, 
turpentine, chloroform, or xylene. If the solution becomes too thick, 
it is diluted with benzene, etc., respectively. The resin is incompletely 
soluble in absolute alcohol, hence addition of alcohol to the clear sol. 
in benzene, etc. causes a cloudiness, The balsam should be kept in 
glass-capped wide-mouthed bottles. Before mounting in balsam, sec- 
tions must be soaked in solutions which are miscible with it. Such 
solutions are, clove oil, turpentine, benzene, chloroform, xylene, creo- 
sote, carbolic acid. It would not do, for example, to take a section 
from alcohol, into balsam. Balsam hardens gradually and hence the 
slide is finished when the cover-glass is placed on. 

Dammar: — This is a resin from which solutions are made similar 
to those of Canada balsam, the same kind of solvents being used. 

Glycerin- gelatine. This is a very convenient medium and is often 
used for mounting vegetable sections. Preparation : 42 c.c. water ; 
38 c.c. glycerin ; gelatine 7 grs. ; carbolic acid 1 gr. Soften the gela- 
tine (best French or German) in the water 2 hrs., add the glycerin and 
warm : add the acid, warm and stir % hr. Filter hot through glass 
wool and let cool. It is solid when cold but melts at 35 — 40 C, and 
will keep for years. Before mounting in this medium, objects must be 
gradually brought from weaker to strong glycerin. The gelatin is 
then melted, a drop placed on a warm slide, the section, freed from 
most of the adhering glycerin, placed in it and covered with a warm 
cover glass. When cold, the gelatine solidifies. The slide should then 
be "ringed " with a circle of cement at the edge of the cover-glass. 
This is done by means of a centering turn-table, a camel's hair brush 
dipped in the cement being held at the edge of the cover-glass while 
the slide rotates with the turn-table. 

Carmine stained sections cannot be mounted in gelatine as the car- 
mine is soluble in it. 

Farranf s Medium: — Equal parts by weight of gum acacia, sat. sol. 
arsenious acid, and glycerin. Soak acacia in sol. arsenious acid for 
several days, then add the glycerin. Avoid shaking which causes air 
bubbles. Same method of mounting is employed in this as in case of 
glycerin-gelatine. Slides should be finished with a ring of cement. 

Glycerin : — This is used sometimes as a mounting medium but is 
troublesome on account of the difficulty of enclosing it with cement. 

Fluids for Temporary Mounting of Objects. 

Water is oftenest used. Glycerin, either concentrated or diluted 
to various degrees, is an excellent medium and very often used. A 
good fluid is a mixture of equal parts by vol. of glycerin, alcohol and 
water. 

Other Micro-Reagents. 

Sulphuric Acid : — Strong acid diluted with one fourth its bulk of 
water. 



Elements of Vegetable Microscopy. 31 

Hydrochloric Acid : — Fairly strong solution. Used in connection 
with phloroglucin or aniline hydrochloride as a test for lignified mate- 
rial ; ajso in distinguishing between calc. carbonate and calc. oxalate, 
both being soluble, but the former with effervescence. 

Phenol or Carbolic Acid:— Used as a clearing reagent, also for 
dehydrating specimens when it is not desired to use alcohol. Sections 
may be mounted directly from this intobalsam. Aniline oil may be used 
in the same way. Aniline is kept free from water by placing in it a stick 
of solid caustic potash. 

Schulze's maceration mixture. — Solution of chlorate of potash in 
strong nitric acid. It is used for the isolation of cells. Sections are 
placed in the sol. and gently heated until the reddish color which first 
appears in the tissue has disappeared. The whole is then poured into 
a large quantity of water to stop action and washed well with water. The 
cells will now be found easy to separate. Sections should not be 
carried from alcohol to the mixture but always from water, to avoid 
violent action. Care is needed to stop the action at the right point. 
The work should be done under a fume-hood. 

Preserving Fluids. 

1. Alcohol. Pass objects from weaker to stronger solutions. 50 
per cent — 70 per cent— 90 per cent. 

2. Glycerin. Pass from weaker to stronger glycerin. 

3. One per cent sol. carbolic acid in water. 

4. Aqueous sol. corrosive sublimate. 

Section Cutting. 

Only very thin objects are suited for examination under the micro- 
scope and the higher the power, the thinner must be the object. It is 
evident that, in order to study large bodies, as the organs of plants, 
thin slices or "sections" must be made. Such sections should be of 
as nearly equal thickness in all parts as possible. A transverse section 
is one at right angles to the long axis of the object. A longitudinal 
section is one parallel to the long axis of the object. In the case of 
cylindrical objects, as a stem, there are two kinds ; — 

1. Longitudinal radial sec Hon, which lies in the plane of the radius. 

2. Lo7igitudinal tangential section, which is parallel to a plane 
tangent to the cylinder. 

The razor must always be keen-edged and should be stropped fre- 
quently to keep it thus, and, when necessary, honed. It is impossible to 
cut a thin section with a dull razor. A razor flat on one side is the best. 
It should always be cleaned after cutting sections. It should be pushed, 
rather than drawn, through the object, with an oblique or sliding mo- 
tion, even and steady and never with a to-and-fro, or sawing motion. 

Sections may be cut free-hand or by the use of a so-called " micro- 
tome " or section-cutter, a machine in which the object is clamped in a 



32 Elements of Vegetable Microscopy, 

jaw which is raised by an accurate screw, while the razor, either held by 
the hand or clamped in a carriage, slides through it, giving very even 
and thin sections. . 

Free-hand sections. — 

If the object is large, it is held in the left hand between the thumb 
and forefinger, the latter being extended slightly, so as to form a rest for 
the razor-blade, which is held in.the right hand. 

Small objects are held in elder or sunflower pith which is split lon- 
gitudinally in halves. The object is left protruding slightly, or both 
object and pith are cut together. 

In most cases it is best, in cutting, to keep the knife-blade wet with 
alcohol or a mixture of equal parts of alcohol and glycerin. Sections 
of fresh tissues or of those that have been kept in any of the preserving 
fluids, should, immediately after cutting, be transferred — best by means 
of a camel's hair brush — to water or alcohol, otherwise air will get into 
the cells and seriously impair the value of the section for study. In re- 
gard to cutting sections with the microtome, practice under the eye of 
an instructor is the best teacher. 

Operations Involved in Making a Permanent Mount of a 

Section. 

Fixing and Hardening ; - in many cases plant tissues are sectioned 
and examined in the fresh state. But often the contents of cells, in the 
living state are too transparent to be seen distinctly and must be killed 
in order to make them more opaque and easily seen under the micro- 
scope. Again, portions of plants may be too soft to be cut, without 
first being put through a hardening process. In all cases where it is de- 
sired to make permanent mounts or slides of tissues, the protoplasm is 
first killed and then hardened, unless the tissue consists of cells already 
dead, for ex., wood cells, stone cells of nuts, etc. The object of killing 
the protoplasm is, as just stated, to make it more opaque and at the 
same time, to preserve its structure for a long time. The process is 
termed fixing. The protoplasm is fixed or coagulated. 

After fixing, the object must often be hardened for cutting. There 
are various reagents for fixing and hardening, some of which do both 
at the same time, while others only fix or kill. (See under the respec- 
tive reagents for fixing and hardening tissues, page 28.) 

Although there are a number of such reagents, those actually used, 
especially in botany, are few. Alcohol is used in nearly all cases. 
Tender objects must never be placed at once in strong alcohol. (See al- 
cohol, page 28.) 

Softening of objects : — See page 29. 

Staining of Microscopic Objects. 

It often happens that some objects, even after fixing, are so trans- 
parent that their structure cannot easily be made out. The more a trans- 



Elements of Vegetable Microscopy. 33 

parent body approaches in its refractive power on light, the medium in 
which it lies, the more difficult it is to be seen. Finally, when the re- 
fracting power is the same as that of the medium, the object is invisi- 
ble. Ex. shells of Diatoms in glycerin are invisible, the refractive indi- 
ces of both being 1.43. By staining or coloring the transparent parts of 
an object, these become visible and their structure is easily made out. 
In a heterogeneous section, like that of a plant stem for example, the 
chemically different materials in it select different stains, so that 
by a contrast of colors a great deal more is learnt than by study of the 
unstained section. The different stains require different lengths of 
time for action which is best learnt by actual work with them. Some 
of them are permanent, others only temporary. The stains fall into 
groups, as aniline, carmine, hematoxylin stains, (See under stains). 

Clearing of Objects. 

In most cases, even after making very thin sections, these are too 
opaque and obscure for observation with the higher powers of the mic- 
roscope and consequently must be made more transparent, that is, 
must be cleared. Some objects are naturally very opaque, as pollen 
grains, spores ; such objects must always be cleared before studying 
them. It often happens that it is desired to study the cell-walls only 
of a section, but this is impossible because of the dense mass of cell 
contents, as starch, protoplasm, oil, resin, milk-sap, etc., which must 
first be removed by special clearing reagents. (See the various clear- 
ings reagents page 29.) 

Mounting of Objects. 

If objects are not intended to be kept for a long time they are 
mounted in water, alcohol, dilute glycerin or concentrated glycerin or 
some other suitable material. For permanent mounting, they are 
usually placed in a medium which solidifies after a time, such as bal- 
sam, glycerin-gelatine, which are most commonly used. The handiest 
is the second because of the little preliminary treatment necessary. 
The object, in whatever medium it is to be mounted, must be saturated 
with a fluid not very different from the mounting medium. For ex. 
to mount in gelatine, the object must be transferred from glycerin ; in 
balsam, from cloves, turpentine etc.; in Farrant's medium, from gly- 
cerin. Media which do not harden or which absorb moisture as gly- 
cerin-gelatine, must be closed in with a ring of cement. (See mount- 
ing media page 30.) 

Scheme for Making Permanent Mounts. 

The specimens are supposed to be alcoholic. If not, they are to be 
placed for a time in dilute alcohol. Alcoholic objects take the stains 
better than fresh tissues. 



34 Elements of Vegetable Microscopy. 

For Balsam Mounts. 

i. Object is killed or fixed in alcohol. 

2. Wash in water if object is to be stained in aqueous stains. 

3. Stain (time varying according to nature and strength of stains) ; 
examine from time to time by transferring to water and noting the depth 
of color. Choose stains according to nature of cells that it is desired 
to stain. Aniline stains color chiefly woody or lignified material. If 
the stains are in alcoholic solutions, take objects from alcohol of about 
same strength. 

4. Wash off superfluous stain in water, carefully (best done by 
moving object about). 

5. Dehydrate by passing into 70 per cent alcohol 3 minutes, 90 
per cent alcohol 5 minutes, abs. alcohol (distilled from lime) 5 or more 
minutes. 

6. Place object in clearing reagent, best oil of cloves, or turpentine 
5 minutes or more. If section is not completely dehydrated, it will now 
appear opaque. It must then be passed back to the absolute alcohol 
and back again to the clearing reagent. 

7. Mount in balsam. (Avoid air bubbles.) Remove first the ex- 
cess of clearing reagent by blotting paper. 

For Glycerin- Gelatine Mounts. 

1, 2, 3, 4, same as above. 

5. Pass into weak glycerin 3-5 minutes. 

6. Pass into stronger glycerin 3-5 minutes. 

7. Pass into cone, glycerin 5 minutes. 

8. Mount in glycerin-gelatine, as directed on page 30, removing 
first excess of glycerin. 

9. Ring slide with cement, (Asphaltum, Brunswick black, etc.) 



CHAPTER X. 
Lesson VII. Tissues of the Higher Plants. 

While it is true that all the essential phenomena which we call 
vital are manifested within the compass of a single cell, it is also true 
that the manifestation is feeble in comparison with that exhibited by 
cell aggregates, where there is division of labor among cells. All 
the higher plants are such aggregates of cells. The tree, for ex., is 
made up of millions of them, and its life is not the mere aggregate life 
of cells precisely alike, but rather that of sets of cells that have 
come to differ from each other in form and function, but all subserving 
the life of the whole organism. 

These cell-groups, which differ from each other in ways more or 
less important, but each of which is composed of similar cells, are 
called tissues. There is a great variety of tissues, the individual cells 



Elements of Vegetable Microscopy. 35 

of which differ more or less markedly from the typical cell already de- 
scribed. 

It must be remembered, however, that all these tissues originate 
from a single cell, and that each cell of the mature plant, however 
great its deviation from the typical form, approximates the latter very 
closely in its early stages of development. 

The various kinds of tissues are classified into four groups or series. 
I" 1. Parenchyma ; ordinary soft ground tissue. 
I 2. Collenchyma ; thick-angled tissue. 

I. Parenchymatous } 3. Sclerotic parenchyma ; stony tissue. 

Series. 14. Epidermal tissue 

5. Endodermal tissue. 
[_6. Suberous or corky tissue. 

ri. Wood or libriform tissue. 
I 2. Tracheids or vasiform cells. 

II. Prosenchymatous I 3. Ducts or vascular tissues ; There are 

Series. 1 many kinds of ducts, viz., dotted, scalari- 

form, spiral, annular, reticulate, trabecular. 
[4. Hard bast or bast-fibres. 

III. Sieve Series, including only sieve or cribriform tissue. 

IV. Laticiferous Series, including laticiferous or milk-tissue which 
may be simple or complex. 

Not all of the tissues are alive at maturity. Some are dead and 
merely serve as supporting tissues. All of the prosenchymatous series 
are of this nature, being devoid of protoplasm and mechanical in func- 
tion. Likewise sclerotic and suberous tissues. Any one of the higher 
plants will contain most of the above tissues. If we examine stems of 
plants, we find that the tissues are not arranged indiscriminately but 
always follow a definite order. This order in phanerogams is differ- 
ent from that in cryptogams, in exogenous flowering plants, it is differ- 
ent from that in endogenous ones. But in any particular case, the 
order is always the same. Exogens are dicotyledonous plants and are 
characterized by having their stems sharply divided into bark and cen- 
tral wood cylinder, while endogens, or monocotyledonous plants, have 
no sharply defined bark and wood core. 

To get an idea of the various kinds of tissues and the particular 
order of arrangement always met with in exogens, the stem of the 
common Geranium serves very well. The stem of most any other ex- 
ogen would answer, as the Bittersweet, Elder, Willow, Sycamore, 
Maple, Yellow-Parilla, etc. 

Make several thin cross sections of geranium stem, free-hand or by 
the microtome, place one on a slide, add a few drops of chlor-zinc- 
iodine solution and cover. Examine with low power. 

The first thing that strikes one is that the cells differ in size and 
shape, in compactness of arrangement, in thickness of cell-walls, in 
contents, besides that some stain blue while others stain brown. 



36 Elements of Vegetable Microscopy . 

Going from the exterior towards the centre the very first layer of 
cells is the 

1. Epidermis or external bounding tissue, a single tier of closely 
laid and similar cells, interspersed with hairs and having their outer 
walls thickened into a cuticle. 

2. Beneath the epidermis, are several tiers of tabular brick-shaped 
cells, in radial rows, the cells of the outer layers are empty and their 
walls stain brown, while the inner cells may contain protoplasm and 
the walls show some blue color. This is the cork layer. 

3. Collenchyma, next to the cork, consisting of cells quite differ- 
ent in shape and arrangement from the cork cells, with cellulose walls, 
as shown by the blue color with chlor-zinc-iodine, rounded or poly- 
gonal and thickened at the angles where the cells join. The cells are 
rich in protoplasm. 

4. The next layer of cells is ordinary parenchyma or ground tis- 
sue^ a broad zone of large cells, with walls very thin and uniform and 
stained blue, (cellulose), rich in protoplasm and starch contents, globu- 
lar in shape, with small angular interspaces at the angles where the 
cells meet. 

5. Bast fibres, next to the parenchyma, a zone of much smaller, 
angular, very thick-walled cells, stained a deep brown (lignified walls), 
compactly arranged, and free from protoplasmic and starchy contents. 
The bast-fibres are dead and act only as mechanical tissue. 

6. The next layer is a not very broad zone of small-celled tissue 
with blue stained walls. Under high power this is composed of two 
sub-layers ; the outer one consists of larger cells, more rounded, of 
unequal size irregularly arranged, and made up of two kinds of thin- 
walled cells, — sieve-tissue and a variety of parenchmya. These con- 
stitute the so-called soft bast. 

7. The inner layer of the two sub-layers is composed of very 
small cells, rich in protoplasm, very closely packed," in radial rows. 
These are primary meristem cells and form the so-called cambium zone 
of the stem. 

8. Next the cambium is a layer, more or less broad according to 
the age of the stem, composed of cells for the most part like the bast 
fibres (See 5.) and stained brown. These are wood or libriform fibres 
(lignified). Scattered among them are other cells of larger diameter 
whose walls are also thickened and stained brown. These constitute 
the vasiform tissue, composed of ducts and tracheids of various kinds. 
Their function is to strengthen and also to convey nutriment. 

9. Interior to this wood circle, is the pith composed of large celled 
parenchyma, with large inter-cellular spaces, and starchy contents. 
The cells on the exterior are smaller than those towards the centre, 
and more compactly arranged. {See figure 43). 

Make another mount and stain with the phloroglucin and hydro- 
chloric acid mixture. The bast fibres, wood cells, and ducts and trach- 
eids are found to stain red, showing lignified cell-walls. 



Elements of Vegetable Microscopy. 37 

Make a longitudinal radial section and examine as before. The 
cork-cells look about the same as in cross section ; the collenchyma 
cells are elongated ; the bast fibres, wood cells and ducts are very 
much elongated and oblique ended or tapering. 

Examine cross sections of other exogenous plants. 

Make permanent mounts of sections stained in haematoxylin and 
fuchsine, also in methyl-green and eosin. 



CHAPTER XI. 
Lesson VIII. — Parenchyma Tissue. 

The parenchymatous series, to which ordinary parenchyma be- 
longs, is characterized by the fact that the cells are less modified, in 
shape at least, from the primitive or typical cells, than the other tissues. 
They mostly retain to maturity the proper character of cells, viz., they 
possess protoplasm and a nucleus and the power of cell division. In 
some cases, they become elongated and somewhat fibrous, but more 
commonly they are not much longer than broad, and have their ends 
square or rounded rather than oblique or tapering. Many of the series 
are thin-walled tissues, but others have the cell-walls thickened by cel- 
lulose, cutinous or ligneous deposits. 

Ordinary parenchyma, or soft tissue, is at once the most abundant 
and the least modified of all the vegetable tissues. The walls are thin 
and frequently, though not always, composed of unmodified cellulose, 
commonly spheroidal or polyhedral in form and the longitudinal rarely 
exceeds the transverse diameter. It includes most of the soft tissues 
of plants, such as the green cells of the leaf, the cells of pith, a consid- 
erable portion of the cells of bark, etc. Sometimes, the cell-walls 
are unequally thickened so as to present the appearance of markings of 
various kinds ; indeed, they are seldom of uniform thickness, but com- 
monly their membranous character and transparency make them 
appear so. 

Make a cross section of pumpkin stem and stain with chlor-zinc- 
iodine. 

The description of the typical cell in Lesson VI answers very well 
for parenchyma cells in the section. One structure not noted there 
will be found here as well as in all green parenchyma, viz., small 
rounded granules stained deep brown, the chloroplasts or chlorophyll 
bodies. In the fresh unstained cell, these are green. The chlorophyll 
granules give the green color to leaves, etc. 

Another difference is the presence of small intercellular spaces be- 
tween the cells, not found in the onion epidermis or any epidermis in 
fact. Also the presence of starch. On careful examination with the 
high power, the blue wall will be found punctate with nearly colorless 
dots. These are thin places or pits in the walls. 

Study also parenchyma of the geranium stem. 



38 Elements of Vegetable Microscopy. 

Ordinary parenchyma occurs in several modifications, such as 
Stellate, or star-shaped cells. 
Folded, cell walls have internal folds. 
Spongy, cells very loosely arranged as in leaves. 
Palisade, cells elongated and arranged like posts. 
Pitted, walls pitted or marked by thin places of various shapes 
and dimensions. 

Pitted parenchyma occurs in a number of plants. It is very easy to 
study in the Sago Palm, (cycas revoluta). 

Make a transverse section of the petiole and examine with high 
power, unstained, in water. 

Thick-walled rounded parenchyma cells will be found with a num- 
ber of transparent, rounded areas looking like holes in the wall. These 
are thin portions of the otherwise thickened walls, and not holes. On 
the edges, the pits cause a beaded appearance, {see figtire 48). Phlo- 
roglucin shows that the walls are somewhat lignified, giving a red color. 
Beautiful permanent mounts may be made by staining in fuchsine 
and eosin. 

Some of the other varieties of parenchyma will be studied later. 



CHAPTER XII. 
Lesson IX. Collenchyma. 

Collenchyma, or thick-angled tissue, is closely related to ordinary 
parenchyma, but the cells are more elongated, often five or six times 
longer than broad, prismatic in shape and thickened at the angles. 
The thickenings are usually not lignified and the cells contain proto- 
plasm, a nucleus and more or less chlorophyll. They are never found 
elsewhere than in close proximity to the epidermis, or rarely in a simi- 
lar relation to endodermal tissue, and one of the uses of the cells is 
evidently that of giving strength to the epidermis. Sometimes collen- 
chyma forms a continuous circle as in the petiole of Begonia and Grape, 
at other times, it forms longitudinal bands, as in stem of Yellow Dock 
and Cow-parsnip. 

The thickenings of the cell walls, in some plants, are excessive and 
strongly diminish the cell lumen, in others, they are slight. Sometimes 
they are confined to the angles, while, at others, they extend to a less 
degree to the rest of the cell wall. 

Make cross sections of the petiole of a Begonia, or Burdock, or any 
species of Grape, and mount in iodine solution. 

Note, the collenchyma, thick-angled cells just beneath the epider- 
mis, containing protoplasm and nucleus ; the character of thickenings ; 
whether the tissue forms a complete circle or occurs in patches, {see 
figure 45.) Add sulphuric acid and note that the walls are cellulose. 
Mount another section in iodine solution and examine with high power 
carefully. 



Eleme?its of Vegetable Microscopy. 39 

The thickenings are marked with delicate stratification lines. Such 
lines are common to thick walls generally and are due to the different 
layers containing different amounts of water, as may be proved by im- 
mersing in strong alcohol, which removes all the water, when the lines 
will disappear. Collenchyma is absent in most Monocotyledons. In 
longitudinal section, the cells present quite a different appearance. 
The thickenings appear as long narrow bands, the cells are elongated, 
some being twice, others five to six times as long as broad, and blunt 
ended. In some plants collenchyma tends strongly to fibrous tissue, 
being very long and greatly thickened and taper pointed. 

A good way to get a longitudinal view of the cells is to strip off the 
epidermis from a Lily petiole, the collenchyma cells will come off with 
it and may readily be studied in water or iodine solution. 



CHAPTER XIII. 

Lesson X. Sclerotic Cells. 

The cells of this tissue are commonly called stone or grit cells. 
The cells differ from ordinary parenchyma ones in having the walls 
excessively thickened, so much so frequently, that the cavity of 
the cell is nearly obliterated. Every gradation, however, may be 
observed between these and ordinary parenchyma. The walls of scle- 
rotic cells are usually lignified and the thickening is deposited in layers, 
giving the appearance of concentric rings. These are the cells which 
give the great hardness to the outer coats of seeds, and the shells of 
nuts. They constitute the gritty particles that occur in the flesh of 
some fruits, as the pear and apple, and are present in many barks, as 
Cinnamon, Oak, etc. 

Sclerotic Tissue of Walnut Shell. 

Use a piece of shell that has been softened by long soaking in 10 
per cent alkali and washed in acidified water. Cut thin sections in 
various directions, taking care not to let the razor run too deep. Mount 
in water and examine with low power, picking out the thinnest edge. 

There will be seen a mass of rounded, somewhat polyhedral cells, 
pressed so close together that no intercellular spaces are visible. The 
walls are extremely thickened, and contain minute dots, as well as 
radial lines connecting the small cavity or lumen of the cell with the 
middle lamella. 

Put on high power. The radial lines can now be seen to be tubes, 
and the dots are tubes cut cross-wise, the ends appearing as dots. The 
tubes are known as pore-canals and are analogous to the pits in ordi- 
nary parenchyma cells. They probably serve to help the circulation of 
nutritive fluids from one cell to another, as is evidenced by the fact 
that the tubes of neighboring cells end opposite each other. (See 
figure 46.) 



40 Elements of Vegetable Microscopy. 

With careful examination, the walls are seen to be made up of con- 
centric layers. These are made more distinct by adding a drop of 
chloral-hydrate solution, (5 chloral-hydrate to 2 water) and watching 
closely its swelling action. The lines come out plainly at first but after 
a time disappear, owing to continued swelling. 

Examining sections cut in various directions from the shell, it will 
be found that the cells have the same general appearance, showing that 
they are, in form, essentially like parenchyma cells ; the difference be- 
ing that the walls are immensely thickened in stone cells, and they no 
longer take part in the vital processes of the plant but act as mechanical 
tissue ; in fact in some cases they are elongated and fusiform so that it 
is difficult to distinguish them from prosenchyma fibres. All grada- 
tions are found between parenchyma and stone cells and between scone 
cells and bast fibres. 

Add phloroglucin and hydrochloric acid to a section and note. 
The walls are stained red, proving lignified material. 

Stone cells may be studied to better advantage by isolating them 
bySchulze's solution as directed under this reagent, page 31. Stain a 
section treated thus with methyl-green and mount in water and tap the 
cover glass with a teasing needle, when the cells will separate in virtue 
of the middle lamellas, which unite the cells, being dissolved away by 
the maceration fluid. 



CHAPTER XIV. 
Lesson XI. Epidermal Tissue. 

This tissue has already been met with in Lesson VI, viz., that of the 
onion scale, but this is not quite a typical example, as there are no 
Stomata, or breathing fiords present which are always found when an 
epidermis is exposed to the air. Since the onion scale epidermis is not 
exposed to the air, there is no need for the pores and they are conse- 
quently absent. In other respects the epidermis of other plants resem- 
bles very much that of the onion. 

The tissue constitutes the primary covering of the plant. It usually 
consists of one, but sometimes of two or three layers of cells. The 
cells are closely packed together, leaving no intercellular space, except 
the breathing pores, and commonly they have that portion of the cell- 
wall which faces exteriorly considerably thickened and cutinized and 
are usually flattened. When seen in surface view, they often appear 
sinuous or irregular in outline, but -sometimes they are straight-sided 
and regular. {See figure 47). In many plants they are somewhat elon- 
gated in the direction of the length of the organ, especially the cells on 
the veins on the under surface of leaves. 

The cells are rich in protoplasm. The different parts that were 
noted in the onion epidermis, are noticed just as plainly in other cases, 
(see Lesson vi). In most plants there are no chlorophyll bodies present 



Elements of Vegetable Microscopy. 41 

in the epidermal cells, to which fact is due their transparency. Ferns 
are exceptions to this. 

Stomata or Breathing Pores. 

These pores are minute apertures, usually surrounded by a pair of 
crescent shaped cells, called Guard-cells. These are much smaller than 
the epidermal cells and are much richer in proteid matters, containing 
a nucleus, protoplasm, numerous chlorophyll bodies and occasionally 
oil globules. 

By means of the pores, the plant exhales the superfluous water 
taken in by the roots and the excess of oxygen not used by it, and 
takes in the carbon dioxide necessary for the plant's life. They always 
open into a large intercellular space. Thus the outside air is in free 
communication with the whole interior of the plant stem and leaves, 
since the air circulates freely through the intercellular spaces which are 
in communication. Communication with the interior of the plant takes 
place only through the pores, since the cutinized exterior of the surface 
of the epidermal cells is highly impermeable to water and air. Hence 
epidermis is an excellent protection against evaporation of moisture 
from the interior of the plant. 

The size of the breathing-pore is regulated by the guard-cells which 
expand or contract according as they absorb or give off moisture. The 
thin radial walls and the thickened outer and inner walls are so devised 
by nature that when, in hot dry weather, moisture is given off by the 
guard-cells to the air, the concave sides enclosing the opening, 
straighten out and thus close it, thereby stopping the further evapora- 
tion. Similarly when the air is moist, the guard-cells absorb moisture, 
and the result is the widening of the pore, and any excess of moisture 
in the interior may escape. 

It is found by suitable tests, that the outer and inner faces of the 
guard cells are thickened and cutinized, while the radial walls are not 
cutinized and. very thin. 

In some cases epidermis is smooth but in the majority of cases it is 
roughened by hairs or glands, and the walls are wavy in outline. The 
number and distribution of stomata varies greatly in different epider- 
mal tissues. They are found principally on the under surface of leaves. 
In some leaves many are found on the upper surface, in others, none at 
all are found. 

Epidermis and stomata of Wandering Jew, and Cultivated Lily. 

Carefully peel off the epidermis from the upper and lower faces of 
a leaf of Wandering Jew. Some of the underlying green cells may be 
torn away with the epidermis but the edges of the piece will generally 
consist of epidermis alone. 

Mount a piece from the upper surface in iodine solution and ex- 
amine with low and high powers. The cells present all the parts 
described in Lesson VI, which see. They are hexagonal in shape. Note 
the absence of stomata, also chlorophyll bodies. 



42 Elements of Vegetable Microscopy. 

Mount a section from the lower surface of the leaf. The epidermal 
cells are the same as on upper surface in shape, etc. Stomata are pres- 
ent, easily distinguished by the two crescentic cells with dense contents 
and chlorophyll granules. {Figure 48). Examine with low and high 
powers. 

Examine epidermis of a Cultivated Lily, and compare with that of 
Wandering Jew. Note the absence of plant hairs from the leaves of 
both plants. 

Cross sections of epidermis will be studied later under leaves. 



CHAPTER XV. 

Lesson XII. Epidermal Appendages. 

All the outgrowths or appendages of the surface of a plant are 
known as Trichomes, which means literally, hairs. They consist of 
one or more cells usually arranged in a row or column, sometimes in a 
mass. The most common forms of trichomes are, — 

1. Hairs, these are the principal form. 

2. Bristles, a single pointed cell or row of cells, much thickened 
and hardened. 

3. Prickles, like bristles, but stouter. 

4. Scales. 

5. Glands, generally short, bearing one or more secreting cells. 

6. Root-hairs, long, thin, single-celled and subterranean. 

7. Sporangia of Pteridophytes. 

8. Ovules of Phanerogams. 

Trichomes originate mostly from the growth of single epidermal 
cells and on their first appearance consist of slightly enlarged and pro- 
truding cells. These may elongate and form single-celled hairs, which 
may be simple or variously branched. The most important of these 
hairs are those which clothe so abundantly the young roots of most of 
the higher plants and to which the name of Root-hairs has been ap- 
plied. These are single cells which have very thin and delicate walls, 
and are the active agents in the absorption of nutritive matters for the 
plant. On the above ground parts, the hairs frequently have the term- 
inal cell developed into a secreting cell, carrying gummy, resinous or 
other products. Such trichomes are known as glandular hairs. 

A good example of simple hairs, which is familiar to every one, is 
the cotton of commerce. Cotton consists of the hairs on the seeds of 
the cotton plant. They have been studied in Lesson I. 

Hairs and Glands as found on a Geranium. 

Make cross sections of the Horse-shoe Geranium stem which need 
not necessarily be very thin. 

Mount one in water and examine the margin with low power. Two 
kinds of hairs will be made out, simple and glandular. (See figure 49). 

Examine with high power. — 



Elements of Vegetable Microscopy. 4S 

The simple hairs are very long, consisting of a row of tapering 
cells which contain transparent protoplasm and nucleus, easily seen by 
applying iodine solution. The end cell is long and pointed. The hair 
fits in among the epidermal cells. 

There are three kinds of gland hairs. 

One kind is rather long, consisting of a stalk of about six cells 
(count the actual number) terminated by a larger gland cell, which is 
round and full of contents. The two or three cells just below the 
gland cell are suddenly narrowed. On the top of the gland cell, there 
is a crescent shaped glistening mass which is found to lie in the cell" 
wall itself, between the outer and inner layers. This mass dissolves on 
applying alcohol or ether, which indicates that it is probably resinous. 
Additional evidence of this is given by the reaction with alcannin solu- 
tion, which stains the mass red. Soak some sections 20 — 30 minutes in 
alcohol (strong), also in alcannin sol. and note results. 

The resinous matter is secreted by the cell and forced out into the 
cell-wall, where it accumulates. 

Iodine shows the presence of protoplasm in the cells. Try to make 
out the nuclei. 

The other two kinds of gland-hairs are very short. One has an 
oblong gland while the gland cell of the other is round. Note the num- 
ber of cells in the stalk of each. The cells are very short. 

Note which of the three kinds is most abundant. 

Submit a section to the action of chlor-zinc-iodine solution for 
about half an hour and then examine. The outer layer of the walls of 
the hair-cells is stained brown, showing cutinization, the inner portion 
of the walls may be blue, showing cellulose subtance. 

Try the clearing effect of chloral-hydrate sol. on the gland-hairs. 
The contents will gradually disappear leaving the cell-wall distinct, 
and the gland cell structure may now be studied. 

It is thought that the purpose of hairs and glands is to afford pro- 
tection to the plant against insects, etc. The odor of the Geranium is 
due to the secretions of the gland hairs. 



CHAPTER XVI. 

Lesson XIII. Starches. 

The green color of the leaves of plants is due to a colored substance 
called Chlorophyll, which is diffused through certain proteid granules 
in the cells. The function of this substance is to utilize the energy of the 
sun's rays in converting carbon dioxide, the main food material of plants, 
into some form of carbohydrate. Starch is a carbohydrate, but that 
formed by the green coloring matter from carbon dioxide is not starch. 
The carbohydrate in question is combined with nitrogen and sulphur, 
(taken up by the plant in the form of salts), into a proteid by the vital 



44 Eleme?its of Vegetable Microscopy. 

processes of the cells. It is not known what the composition of the 
carbohydrate is, nor the processes involved in building up the proteid 
substance. 

The starch granules found in chlorophyll bodies were at one time 
supposed to be formed directly from carbon dioxide, but Strasburger has 
clearly shown that this is not true. They result from a breaking down, 
by the chlorophyll bodies, of protoplasm previously formed by those 
bodies. Starch, hence, is a result of a destructive process. It is prob- 
able also that the starch formed by amyloplasts in cells devoid of 
chlorophyll is also formed from proteids. 

There are various reserve food materials found in the plant and 
starch is one of the most important. It is found in various parts of the 
plant, for ex., the stems of certain palms, which are gorged with it, as 
the Sago ; it is the principal substance in tap-roots, root-stocks, corms, 
bulbs, tubers ; many fruits and seeds, as grains, pulses, bananas. 

The power of building up protoplasm from starch is possessed by 
all living cells, whether possessing chlorophyll or not, and independ- 
ent of sun light, but no new carbohydrate is ever formed without light. 
A tuber will sprout and grow in the dark until all the starch is used up 
when growth ceases, and to renew growth, it must be brought out into 
light. 

Description of Starch Grains. 

They are hard and of various sizes and often possess shapes and 
markings sufficiently characteristic to identify the plant from which 
they come. They vary from i to joo or even 200 micro-millimeters, 
(a micro-millimeter= T o 1 o m. m.) and granules from different sources 
have distinct characters. 

Starch grains are simple and compound. 

Examples of simple grains are, potato, wheat, maranta ; of com- 
pound grains, oat, rice, colchicum. 

Nearly all starch grains possess a nucleus or hilum, around which 
the granule is built up in layers which differ from each other in trans- 
parency, owing to different amounts of water in the different layers. 
The layers are concentric or eccentric according as the nucleus is cen- 
tral or placed to one side. Examples of these are, bean starch and 
potato respectively. 

Starch grains differ from one another in a number of ways, some of 
which are the following. 

Size and shape of grains. 

Position of hilum (central or eccentric). 

Number and distinctness of stratification lines. 

Degree to which the hilum is fissured. 

Character of fissure. 

To see the manner in which starch is packed in the cells of the 
various plant organs, examine cross sections of the potato tuber and 
podophyllum rhizome. 



Elements of Vegetable Microscopy. 45 

In the potato section, there are on the exterior a layer of cork cells, 
like rows of bricks. Next these, are some small, closely packed, par- 
enchyma cells, rich in protoplasm, but containing few starch grains and 
these are small. There may also be seen cubical crystals which look 
like mineral crystals, but are proteid as they stain with iodine and are 
dissolved by caustic potash. Farther interior, the cells are very large, 
and filled with large-sized starch grains, and the cubical crystals are 
wanting. 

Apply dilute iodine sol. The grains assume a dark blue color, the 
protoplasm stains brown, and the cubes the same. It will be observed 
that the younger starch grains in the outer small parenchyma cells are 
mostly found in groups. By a special method of preparation, it would 
be seen that the grains are grouped around a mass of proteid granules, 
each one of which is attached to a starch grain. These proteid gran- 
ules are the starch-builders and are called amy lop lasts. They are sim- 
ilar to chlorophyll bodies, and except in a few instances, all starch 
grains are formed by the one or the other kind of these bodies. 

Scrape a slice of potato with a knife and mount in water. The 
grains are ovate, with one end smaller than the other, and a hilum or 
nucleus at the smaller end. The hilum is surrounded first by concen- 
tric lines, which farther away become eccentric. This shows that at 
first the growth of the grain was equal on all sides but afterwards be- 
came much greater on one side than on the other. This view is borne 
out by the fact that in young grains the hilum is central. Nearly all the 
grains are single but some double grains may be found, containing two 
nuclei, each with concentric and eccentric markings about it, and a dis- 
tinct dividing line. Some grains are not double but contain two nuclei, 
i. e., are bi-nucleated. 

The nucleus is usually a circular spot in the potato grain, but some- 
times it is fissured. The small end of the grain, where the nucleus is 
found, is thicker than the broad end, the grain being shaped some- 
what like a clam shell. See figure 50. 

Let a drop of .5 per cent caustic potash sol. run under the cover glass 
and watch the starch grains as the alkali comes in contact with them. 
They swell and at first the layers become more distinct, but after a 
while they grow less distinct and finally disappear. The more watery 
layers at first absorb water, under the action of the potash, more rapidly 
and thus stand out more distinctly. Finally the whole grain dissolves 
and disappears. 

Colchicum Starch .-—Scrape the surface of a dried slice of the corm 
of Colchicum autumnale, and mount the powder in water. 

The grains are much smaller than the potato starch, and usually in 
groups of three or four. Some are single but their flat faces show that 
they belonged to a compound grain. Others are simple grains, and are 
spherical in shape. The hilum is central and strongly and distinctly 
fissured, usually stellately. The lines are difficult to see in these grains. 
{See figure 50). 



46 Elements of Vegetable Microscopy. 

Other Starches. 

A large proportion of the edible starches obtained from the 
rhizomes or root-stocks of various plants are known in commerce un- 
der the name of arrow-root. Properly the name should be restricted to 
the starch yielded by two or three species of Maranta, the chief of 
which is Maranta arundinacea, When genuine or West Indian arrow- 
root is spoken of, it is understood that this is the variety meant. The 
granules are ovoid and marked with lines very similar to potato starch 
grains, but more faint and less distinct, and the average size is smaller. 
The hilum is at the middle or thick end of the grain and is fissured. 
{See figure 56). 

Tous-les-mois or Tulema arrow-root, is obtained from several spe- 
cies of Canna, a genus closely allied to Maranta (the granules are very 
large). 

East Indian arrow-root, obtained from the root stocks of several 
-species of the genus Curcuma (Zingiberaceae) chiefly Curcuma angus- 
tifolia. 

Brazilian arrow-root, starch of the cassava plant — Jatropha mani- 
hot. (Tapioca of commerce). 

In tapioca, most of the grains are blurred, which is due to the 
heating in the process of manufacture, but many grains will be found 
uninjured. 

British arrow-root, potato starch, sometimes sold under this name. 
The French excel in the preparation of imitations of the more costly 
starches from potato starch. Its chief use, however, as an edible 
starch, is for adulterating other more costly preparations. It can 
easily be distinguished under the microscope. 

Other common starches are sago, rice, wheat, corn, oat. 

Rice and oat starches are compound granules. They are very 
much alike in the form and shape both of the compound granules as 
well as the component grains. For the starches See figure 50. 

CHAPTER XVII. 
Lesson XIV. Aleurone Grains. 

Protoplasm exists both as active and inactive. In the active state, 
as found in actively growing cells, it exhibits vital phenomena in a 
marked degree, but as found in the cells of seeds, tubers, and thick- 
ened roots, it exhibits few signs of vitality, contains comparatively little 
water and its condition approximates that of a solid. 

Ordinary protoplasm is formless ; even under the highest powers, it 
exhibits no structure except the presence of numerous very minute 
granular bodies called microsomes, the nature and uses of which are not 
yet understood. It passes however into several modifications which 
exhibit a more or less characteristic structure. The most important of 
these is the chlorophyll body. The amyloplasts, spoken of under starch, 
are another form with structure. These are active forms of protoplasm. 



Elements of Vegetable Microscopy. 47 

Aleurone grains are a structural form of inactive protoplasm, the 
use of which is to act as reserve food material. Plants lay up a store of 
food in various forms, one of which we have studied i. e., starch. Other 
non-proteid food materials are, oil, inulin, sugar. Some albuminous 
forms are also stored up, the most important of which are aleurone 
grains. These are found chiefly in seeds and most abundantly in oily 
ones. They are usually rounded granules, often very small, but some- 
times quite large, as in Croton and Castor beans and in the Brazil-nut. 
In some cases, the granules appear homogeneous in structure as in 
peony, almond, cherry and apple seeds ; in other cases, they contain 
various substances, as oily matters, mineral crystals, and crystalloids, 
as in Brazil nut, pumpkin seed, castor bean, walnut. 

Castor Bean. 

Remove the hard seed-coat of the bean and make thin sections of 
the endosperm. 

Mount one- in strong glycerin and examine with low and high 
powers. Not much will be made out with low power. The cells will be 
seen to be crowded with rounded granules, looking much like starch. 
{See figure 51). 

Under high power, rounded or ellipsoid bodies, imbedded in a finely 
granular matter, fill the cells. These are the aleurone grains. After 
a little time the clearing effect of the glycerin shows that the grains are 
not homogeneous but contain a denser, polygonal body looking like a 
crystal, and known as a crystalloid, which varies in size, being often 
nearly as large as the grain. Lying alongside of this, is seen a glob- 
ular body, strongly refractive and composed of magnesium and cal- 
cium phosphates, and known as a globoid, {figure 5/). 

Add strong iodine solution to the section in glycerin. The grains 
stain brown, especially deep in the crystalloid, indicating the proteid 
nature of the latter. The globoids remain unstained. 

There is no blue coloration, showing the absence of starch. 

Mount a fresh section in water and watch the aleurone grains. 
The ground substance soon swells and dissolves, leaving the crystal- 
loid standing out more distinct. After a time this also swells and loses 
its angles and finally disappears. Oil globules may also be seen to 
collect and run out from the ruptured cells. These have a refractive 
appearance, being bounded by a dark band. 

If fresh sections be mounted in alcannin, or cyanin solution, the oil 
globules will stain after a time deep red or blue. Oil is a reserve food 
for the plant, like starch and aleurone, and is found in a great many 
seeds and spores, often in large quantity. 



4 8 Elements of Vegetable Microscopy. 

CHAPTER XVIII. 

Lesson XV. Chloroplasts or Chlorophyll Corpuscles. 

When speaking of starch, it was noted what importance these bod- 
ies are to the life of plants, and that without them, plants could not 
exist. They are the most important structural form of protoplasm. 
They are the bodies which give the green color to plants and are com- 
monly rounded, oblong or flattened in shape. An odd form is the 
spiral bands found in Spirogyra, (which see). 

Chloroplasts are proteid in nature, having the power of growth and 
division, and always closely associated with ordinary protoplasm, and 
are hence to be regarded as part of the living protoplasm. 

In many plants, chloroplasts are small and difficult to study, but in 
others they are easily studied. 

Most any moss, the prothallia of ferns, Eel-grass, Water-weed, are 
excellent objects of study. 

Mount a few fresh leaves of a moss in water, and examine the cells 
lying near the edge of the leaf. The cells contain numerous rounded 
greenish bodies, the chlorophyll bodies. Note the closely packed, rec- 
tangular shaped, somewhat thick-walled cells. Try to observe chloro- 
phyll bodies that are constricted in the middle. Such are in the act of 
division. {Figure 52). 

Run strong alcohol under the coverglass. The green bodies are 
slowly bleached, the chlorophyll is dissolved out and forms a greenish 
solution in the cells. From this experiment it is concluded that the 
bodies consist of two parts, a proteid ground work, through which is 
diffused the chlorophyll or green color substance. 

Add iodine sol. to a leaf that has been bleached with alcohol. The 
transparent protoplasm of the cells is now stained brown and made 
visible. The ground substance of the chloroplasts also stains brown, 
indicating a proteid substance. 

Starch grains in chloroplasts. Put some leaves of a vigorously 
growing moss that has been exposed to sunlight for two or three hours,, 
in alcohol until bleached. Then mount a leaf in water, focus on it, and 
apply a drop of chloral-hydrate iodine solution at the edge of the cover 
glass, and watch closely the chlorophyll body as the reagent comes in 
contact with it. The ground substance is seen to swell rapidly and 
becomes transparent, leaving the starch grains, stained blue, visible. 
The latter are small and elongated. By the continued action of the 
chloral, the whole structure gradually disappears. The starch that is 
formed in the chlorophyll bodies in the day time, is dissolved during 
the night and transferred to other parts of the plant. 

CHAPTER XIX. 

Lesson XVI. Secretion Sacs, Intercellular Air Spaces, 
and Secretion Reservoirs. 

Some cells at maturity, lose their protoplasm and their proper 



Elements of Vegetable Microscopy. 49 

cellular character and become filled with secreted matters. These 
form the secretion sacs. They are of various forms, but more com- 
monly resemble parenchyma cells in appearance and character of their 
walls. Sometimes they are much elongated and resemble latex tissue. 
The sacs are given names according to the secretion they contain, thus, 
resin sacs, mucilage sacs., etc. 

Intercellular air spaces are more or less abundant in nearly all 
multicellular plants, their probable function being to supply air to the 
interior tissues for respiratory purposes. In aquatics, the spaces are 
usually large and often regular in shape, while in most terrestrial plants 
they are small and angular. Air spaces are of two kinds, — Schizoge- 
nous and Lysigenous. The former are formed by the splitting of the 
cell-wall common to two or three cells. The latter result from the 
breaking down of some cells, leaving a space. Secretion reservoirs or 
canals and intercellular air spaces differ from each other only in their 
contents, the former containing resins, gums, oleo-resins, etc., the 
latter only air. 

Intercellular Air Spaces and Resin Sacs in Rhizome 
of Calamus (Sweet Flag). 

Make thin cross-sections of the fresh rhizome or of the dried one, 
after having soaked it for some time in water to soften it. Mount in 
water and examine the outer third of the section. The parenchyma 
cells are loosely arranged in chains with large and tolerably regular 
intercellular air spaces. Most of the cells are filled with starch grains 
together with protoplasm and nucleus, but, scattered here and there 
among these, are larger spherical cells, filled with a refractive or glisten- 
ing material, sometimes intermixed with a brownish solid. These are 
the secretion sacs, ( figure 33). The refractive contents of the sacs are 
not saponified by caustic potash which fact indicates a volatile oil. 

P'urther evidence in favor of this conclusion is given by applying 
cyanin solution to a section, when, after some time, the contents are 
stained blue. The solid brown matter found in some of the cells is 
resin and also stains blue with cyanin. 

Mucilage Sacs in the Root of Marshmallow. 
Make cross sections of the root, and place in alcohol (not in water! 
Mount a section in a drop of glycerin and examine the parenchyma 
tissue. The cells are small and densely filled with starch grains. Scat- 
tered irregularly among these are numerous larger rounded sacs con- 
taining a transparent substance — the mucilage sacs. Add a drop of 
iodine solution to a fresh section. The contents of the sacs do not stain, 
showing absence of any proteid matter. To the same section add now 
a drop of sulphuric acid. The mucilage is stained a deep brown, ^nd 
the walls blue (cellulose). Under favorable conditions delicate, concen- 
tric lines may be seen in the mucilaginous contents. In longitudinal 
sections, the sacs are somewhat longer than broad. The cells are 
modified parenchyma cells. 



5<d Elements of Vegetable Microscopy. 

Mucilage and Raphide Sacs in Squill Bulb. 

Crystals are of such general occurrence in widely different orders of 
the higher plants, that there are perhaps none in which they may not 
be detected. They have been found in nearly all parts of the vege- 
table structure, more commonly in the interior of parenchyma cells, 
sometimes in specialized crystal-cells. 

They occur either singly or in groups. The most common forms 
are the octahedron and the prism. Sometimes the crystals are much 
elongated and pointed, like a needle, and are then known as raphides, 
(from raphis, a needle). These are generally massed in a compact 
bundle, like a wheat-sheaf, occupying a large part of the interior of the 
cell. Raphides are by no means of such general occurrence as ordi- 
nary crystals, being restricted to certain orders. 

Soak a slice of the scale of squill bulb in water just long enough to 
soften it and then place in a mixture of alcohol and glycerin 6-8 hours. 
Make thin sections and mount in glycerin. The tissue is composed of 
large, clear, typical parenchyma cells, with here and there a cell filled 
with long needle crystals or raphides, together with mucilage. {See 
figure 54). 

Apply a drop of acetic acid. The needles do not dissolve. To 
another section, add hydrochloric acid ; the needles dissolve without 
effervescence, showing that they are calcium oxalate. Had they been 
carbonate, they would have dissolved in acetic acid with effervescence. 

Secretion Reservoirs. 

These differ from intercellular air space only in being filled with 
secretions instead of air. They differ from secretion sacs in that they 
are spaces surrounded by a number of cells, while the sacs are single 
cells. The reservoirs are often merely irregular spaces left by the 
breaking down of one or more cells, but they sometimes have a 
remarkable regularity of form and clearness of outline. 

It has been observed that these spaces are not, as a rule, met with 
in plants having the simple secretion sacs. The cells which surround 
the more complete cavities are quite different from the other paren- 
chyma cells, and they are collectively called the epithelium of the 
spaces. These are the secreting cells and the secreted matters are 
discharged, in some manner, into the reservoirs where they accumulate. 

Soften the bark of the rhizome of Wild Sarsaparilla, (Aralia nudi- 
caulis) by wrapping the rhizome in wet filter paper for some time. 
Make cross-sections of the bark and mount in water. 

Among the loose parenchyma cells are large regular spaces, sur- 
rounded by a layer of cells, smaller than the rest of the parenchyma 
cells and more densely filled with granular matter. These are the epi- 
thelium secreting cells. Many of the reservoirs may be empty, but 
some will be found containing a large lump of brown resin. {Figure 55). 

In longitudinal section, the reservoirs are long, unbranched, 
straight, cylindrical spaces, running lengthwise of the rhizome. 



Elements of Vegetable Microscopy. 51 

Reservoirs resemble the sacs in regard to the nature of the secre- 
tions they contain. Some contain mucilage, others, resin, or oleo-resin, 
etc. They are also schizogenous or lysigenous in origin, like the air 
spaces. 



CHAPTER XX. 

Lesson XVII. Wood Cells, or Libriform Tissue and Bast Fibres, 

or Liber Fibres. 

These fibres belong to the prosenchymatous series of tissues. 
Some of the tissues of the parenchymatous series have been consid- 
ered, viz., ordinary parenchyma, collenchyma, sclerotic, epidermal, and 
the general characteristics of the series have been discussed. (See 
under ordinary parenchyma). 

To the prosenchymatous series belong those cells which at matur- 
ity lose their nuclei and protoplasm, and therefore their distinctively 
cellular character, and have their walls thickened by secondary depos- 
its. They sometimes contain starch and traces of proteid matter but 
take no active part in the nutritive processes of the plant. They serve 
it mainly for strengthening or supporting and hence have been called 
mechanical tissues. They are serviceable also in conducting the sap. 
The elements of these tissues are for the most part elongated and 
oblique-ended, or taper-pointed. Among the shorter cells, transitions 
occur. Between them and sclerotic parenchyma and between the fib- 
rous forms and collenchyma, every gradation may be found. 

Wood-cells are found in the so-called fibro-vascular bundles of the 
plant, and in that portion known as the xylem. They are the thick- 
walled, fibrous cells, which are not tracheary in nature. It will be nec- 
essary to explain these terms. 

The fibro-vascular bundles constitute the fibrous frame-work of the 
plant, corresponding somewhat to the bony skeleton of the human 
body. In the leaf, they are the system of veins, and in the stem and 
root, the tough resistant portions. Their function is partly to give 
strength and partly to conduct the fluids of the plant. The cells com- 
posing the bundles, therefore, for the most part, have their walls thick- 
ened and are elongated in the direction of the length of the organ 
bearing them. They belong chiefly to the prosenchymatous series, al- 
though other tissues are commonly included in the bundles. In some 
plants, as the stem of the Indian Corn and the petiole of the Plantain, 
the bundles may be readily separated in the form of tough, stringy, 
masses from, the softer surrounding tissue. 

(Break the petiole of a Plantain leaf and note the tough threads 
protruding from the broken end. These are the bundles). 

Although a number of kinds of tissue are usually found in the fibro- 
vascular bundles, only two kinds are really essential, viz., ducts, (and 
tracheids, which may be regarded as imperfectly formed ducts), and 



52 Elements of Vegetable Microscopy. 

sieve cells. These and their associated tissues always constitute sepa- 
rate longitudinal portions of the bundle. The nature of ducts and 
sieve cells will be explained later. The portion of the bundle to which 
the ducts belong is called the xylem which means the wood, and that 
to which the sieve cells belong is called the phloem or bast (phloem 
means bark). The reason for calling this the bast or bark is the fact 
that the inner bark of gymnosperms and dicotyledons, also called the 
bast layer, is composed of the phloem portions of the bundles, which 
are arranged in a circle. Inside of these are the xylem portions of the 
bundles, forming the cylinder of wood. {See figure 56). 

The term bast was originally given to the inner bark of the Linden 
tree, which was called Bass-wood tree. It is now applied to the inner 
layer of any bark. 

The term liber, which is also given to the inner or bast layer, was 
applied in a more general way, to any smooth inner bark upon which 
one could write (Liber is the latin for book). 

The peculiar, long, tough, thick-walled cells which impart the tough- 
ness to the inner bark, making it valuable in the arts, are hence known 
as bast or liber fibres. It is in the bark of dicotyledons that liber cells 
or fibres occur most abundantly, in the phloem portions of the bundles. 

The term libriform has reference to the general resemblance of 
wood fibres to bast or liber-fibres. Some plants, for ex., the monocotyls, 
have no true bark, consequently the bast or phloem portions of the 
bundles do not lie in the inner or bast layer of the bark, and the bast 
fibres of such bundles are apparently misnamed. However the term 
liber or bast fibres has been extended to embrace all those fibres that 
occur in the phloem portions of the bundles whether they occur in the 
inner bark or elsewhere in the plant, and whether they occur in gymnos- 
perms, dicotyls, or monocotyls. 

Libriform or wood fibres usually differ from liber fibres in being 
relatively less elongated, less tough and flexible, and less strongly lig- 
nified at maturity, but there are many exceptions, especially in mono- 
cotyls, where the two tissues are often indistinguishable by structure 
alone. The fibres vary often in length. 

As w r as said before, wood fibres occur in the xylem of bundles and 
bast fibres in the phloem. 

These may be conveniently studied in the Geranium stem in cross 
and longitudinal sections. They have already been noted superficially 
in Lesson VII. 

Make thin cross sections of a geranium stem and study without stain- 
ing and also by staining with phloroglucin and hydrochloric acid (red). 

The wood circle lies within the cambium zone and surrounds a cen- 
tral area of parenchyma cells, the pith. (See Lesson VII). 

It is composed of the xylem portions of numerous bundles which 
have grown together into a solid ring of woody tissue. The wood 
fibres, in cross section, are seen to be very thick-walled, compactly 
arranged, more or less compressed laterally by mutual pressure, so as 



Elements of Vegetable Microscopy. 53 

to appear angular. They lie next to the cambium zone. The cells are 
separated by a distinct line, the middle lamella. The walls are ligni- 
fied, as shown by the red stain, the middle lamella being deeper red 
than the rest of the walls. There are no intercellular spaces. The 
cells are unequal in size and irregularly arranged. There are delicate 
stratification lines and occasionally pore-canals in the walls, though 
these are seen with difficulty. {See figure 57). 

In the woody ring, there are other cells, besides those just de- 
scribed, with much larger openings, the ducts or tracheids, which will 
be described a little later. Woodfibres do not occur in all fibro-vascu- 
lar bundles, but are nearly always present in woody and herbaceous 
dicotyls. 

Bast fibres : — Outside the cambium zone, is another circle of thick- 
walled cells, looking in all respects very much like the wood fibres just 
described. These are the bast or liber fibres. (See Lesson VII). The 
description of the wood fibres answers also for the bast fibres. With 
phloroglucin and hydrochloric acid, they stain red and the middle lam- 
ella deepest. Stratification lines and pore canals can also be seen 
with care. In many cases, bast fibres are not as strongly lignified as 
wood-fibres and take the stains less deeply. In such cases the lignifi- 
cation is chiefly confined to the outer layers of the cell-walls while the 
inner layers are more or less cellulose in nature ; with double stains, 
as methyl-green and eosin, the outer layers will stain green and the 
inner ones reddish. 

Bast fibres are confined not alone to the phloem or bast portion of 
fibro-vascular bundles, but are often found in other portions of the plant ; 
for ex., the strengthening fibres beneath the epidermis of some leaves ; 
in the ground tissue of many vascular cryptogams. As a rule bast 
fibres are thicker-walled than wood fibres, but both kinds may vary 
considerably in the thickness of the walls, in their lengths as compared 
with their diameters, in the number of pore canals. 

Wood and Bast Fibres in Longitudinal Section. 

Treat several longitudinal radial sections of the geranium stem 
with Schulze's macerating fluid, as directed under this reagent. Wash 
in water and stain with methyl-green, taking care not to rupture the 
sections. Mount in water, cover, and tap gently with a teasing needle, 
after having located the position of the bast and wood areas. The mid- 
dle lamellas are dissolved by the Schulze solution, and, by tapping on 
the cover glass, the fibres separate and are easily studied. 

The fibres splice over one another, are very long, the wood fibres 
being often as much as twenty or thirty times as long as wide and the 
bast fibres even longer, the ends taper to a point, sometimes, however, 
abruptly, and at times are forked. The walls are smooth, and, with 
careful staining and good light, delicate slits are seen running obliquely 
across the walls. 1 See figure 58 1. 



54 Elements of Vegetable Microscopy. 

Sometimes bast and wood fibres are found which are made up of a 
row of two or three cells and then they have cross partitions in the lu- 
men or cavity of the fibre. 

Bast Fibres of Cinchona Bark. 

Bast fibres vary greatly in length and lignification. There are some 
extremely long, flexible, slightly lignified fibres, for ex. Flax, Hemp, 
Mezereum, on one extreme, and very short, brittle, much lignified 
fibres on the other extreme, as found in Cinchona bark. 

Make cross and longitudinal sections of Cinchona bark (Calisaya 
or succirubra) that has been softened in water or alkali, and stain in 
methyl-green. 

Cross section. — The fibres are found in the inner layer of the bark,, 
singly or in small clusters. They are excessively thickened, strongly 
lignified, of large diameter, with cavity almost obliterated. The walls 
are divided into layers and these are finely stratified. Pore canals are 
also visible, {figure 59). 

Longitudinal section. — Treat with Schulze's solution, wash, stain 
and mount in water and tap the glass. The fibres are relatively very 
short, being about six times as long as wide, fusiform or wedge-shaped 
on the ends. The cavity appears as a line and the stratification is dis- 
tinct. 



CHAPTER XXI. 
Lesson XVIII. Tracheary Tissue. 

This includes tracheids and ducts. When speaking of the fibro- 
vascular bundles, it was said that the xylem portion of the bundle 
was that which contains the wood cells and tracheids or ducts. The 
peculiarity of tracheary cells is that the walls are thickened unevenly, 
the thick parts being on the inside of the walls and arranged in various 
forms, giving rise to spiral, reticulate, scalariform, annular, dotted, 
ducts, etc. 

The cells of tracheary tissue are usually less thick-walled than wood 
fibres and of larger diameter, and mostly oblique-ended or. blunt. 
These cells have been referred to in Lesson VII. They are more widely 
distributed than wood-fibres as they are found in all vascular plants, 
i. e,, plants containing bundles. (The name fibro-vascular means that 
there are both fibres and vessels or ducts in the bundles). 

Ducts and tracheids are alike in regard to the markings of the 
walls. The difference is that a duct is composed of a row of tracheids 
in which the separating partitions have been absorbed, leaving a duct 
or vessel. A tracheid is a single cell. 



Elements of Vegetable Microscopy. 55 

Tracheary Tissue in Geranium Stem. 

Make longitudinal radial sections and macerate in Schulze's solu- 
tion, wash and stain in methyl-green, mount in water. The following 
ducts may be found, in the xylem of the bundles. 

Reticulate ducts. — So-called because the thickenings in the cell- wall 
are in the form of a network, giving a pitted appearance to the walL 
The walls are somewhat prismatic and the pits occur on the flat sides* 
By means of them, a lateral osmotic circulation is kept up with other 
ducts. 

Notice in some of the ducts, on the oblique ends, large openings 
where one cell communicates with another. {See figure 60). Reticu- 
late ducts are the most numerous in the geranium, as well as most 
plants. 

Spiral ducts. — Widely distributed in plants. The thickening in the 
wall takes place in a perfect spiral, the part between the turns being 
very thin and almost invisible and cellulose in nature. There may be 
two spirals in a duct, one within the other. In other plants, ducts with 
more than two spirals are found. Sometimes the turns of the spirals 
are connected by cross thickenings and then the duct merges into a 
reticulate one. Again the thickenings may be spiral on one end of the 
duct but pass into separate circles on the other, forming an annular 
duct. This kind of duct is found associated with the spirals in the 
Geranium. The two are closely related. The spirals and rings may 
be close together or wide apart, and the rings may be at various incli- 
nations to the length of the duct The spiral ducts are smaller in diam- 
eter than the reticulate. {Figure 60). 

SCALARIFORM DUCTS IN FERNS. 

These ducts have their thickenings arranged like the rounds of a 
ladder, hence the name, scalariform. They occur in many plants but 
they are seen to best advantage in the ferns, where they are beautifully 
developed and almost to the exclusion of all other woody tissue in the 
bundles. 

They also occur well developed in some monocotyls, for ex., the 
Sarsaparillas. 

Make thin longitudinal radial sections of the rhizome of the Male 
Fern or Eagle Fern, stain in methyl-green, or phloroglucin and hydro- 
chloric acid, and mount in water. The ducts will be stained green or 
red ; they are mostly prismatic, or flat sided, where they press upon one 
another, and at the edges where the sides meet, there is a thickened 
ridge. Crossing the flat faces are numerous parallel thick ridges sepa- 
rated by very thin places looking like slits. The faces have the appear- 
ance of a ladder. The ducts are oblique or taper-pointed and the ends 
splice over each other. The ducts are large in diameter. {See figure 66). 

Isolate the ducts by maceration in Schulze's reagent. 



56 Elements of Vegetable Microscopy. 

Tracheary Tissue of Gymnosperms. 

Tracheids with bordered pits. — These peculiar cells, although occa- 
sionally found in other plants, are characteristic of gymnosperms. In 
these plants, ducts and wood cells are rare, being replaced by tracheids 
which constitute nearly the whole of the wood. The tracheids are so 
peculiar in structure that you may distinguish a gymnosperm from other 
plants. A few genera of gymnosperms can be recognized by the num- 
ber and regularity of the markings on the tracheids. 

Tracheids of Pine. 

Make longitudinal radial sections of the wood made soft by soak- 
ing a long time in alkali. This is done by cutting lengthwise at right 
angles to the rings of growth. The tracheids are long tapering fibres, 
similar to wood fibres, but larger. The surfaces of the cells are marked 
by a row of pits, each pit being surrounded by a smaller circle inside 
of a larger one. At times the pits are close together, at other times, 
they are wide apart. {Figure 61). 

Longitudinal Tangential Section. 

In this section, no pits are found on the faces of the cells, but 
occur on the edges. 

Find a pit cut exactly through the middle. It forms a lens-shaped 
cavity in the wall between two cells, opening into the two cell cavities 
by circular orifices which in flat view appear as the inner small circle of 
the pit (see above). Running lengthwise through the pit and closing 
off the cavities of the two neighboring cells, is the middle lamella. 
{See figure 60). 

It will be seen, thus, that the pits are absent from the cell faces 
which face exteriorly and towards the pith while they are on the other 
two faces. 

Here and there, between the tracheids, occur rows of two or three 
rounded cells, which are not to be mistaken for the pits. They are 
much larger, being the lignified parenchyma cells which form the so- 
called medullary rays. Apply chlor-zinc iodine to the sections. 

CHAPTER XXII. 
Lesson XIX. — Laticiferous Tissue. 

Many plants, when wounded, emit a milky fluid varying in color, 
copiousness, consistency and chemical composition in different plants. 
This is called the latex, hence the name laticiferous tissue. This tis- 
sue differs considerably in different plants and is not confined to any 
particular region or tissue system, but it is most common and abundant 
in ordinary parenchyma. 

The cells of milk tissue are of two kinds ; simple and complex or 
branching. 



Elements of Vegetable Microscopy. 57 

The simple latex tubes consist of long cells of indefinite length, 
running lengthwise of the plant, with only a few branches. Each tube 
with its few branches is believed to be a single cell. In cross section 
they are distinguished from parenchyma cells by their smaller diameter, 
and by being filled with opaque and densely granular substances. The 
cell-walls are cellulose. The complex tissue consists of greatly branch- 
ing tubes, the branches uniting cross-wise and forming a complex net- 
work in the plant. 

Latex is of the nature of a waste or excretory product, although it 
contains albumin and carbohydrates. It contains resins and gums in 
solution and oily matters, often alkaloids and organic acids. It coagu- 
lates and forms a sticky mass upon exposure to the air. India rubber 
is an example of such dried latex. 

Stems of plants in which latex tissue is to be studied should be cut 
into pieces and immediately put into strong alcohol which coagulates 
the latex and prevents it from running out of the tubes. 

The simple tissue may be studied in the Euphorbias, Milkweeds, 
etc. 

Make cross sections of one of the milkweeds, stain in methyl- 
green and mount in water. 

The cross-sections of the tubes may be readily recognized in the 
pith and the parenchyma of the bark, by their smaller diameters, and 
densely granular, more deeply stained contents ; the wall of the tubes 
are often thicker than those of the adjacent parenchyma cells. 

Examine a longitudinal section stained in methyl-green. Lying 
among the parenchyma cells, will be found long tubes, filled with 
dense granular matter, wavy and scarcely branching. The branches, 
when present, do not unite with those of a neighboring tube. Each tube, 
however long, is a single cell. Figure 62. 

Apply chlor-zinc iodine. The cell-walls stain blue and the con- 
tents a brown, showing presence of albuminous matter. Alcannin or 
cyanin solutions would show the presence of oily or resinous matters. 
These are held in suspension by emulsion and give the latex the milky 
appearance. 

Complex milk tissue. This is found in Dandelion, Chicory, Cel- 
andine, Poppy, etc. 

Make cross sections of Dandelion and Chicory roots and stain in 
haematoxylin. The milk cells are arranged in small groups and these 
form, in the Dandelion, concentric circles throughout the whole bark, 
which to the naked eye and under low power, seem complete. Under 
high power the circles are interrupted here and there. In Chicory, 
the milk tubes are arranged in radiating lines through the bark, and by 
means of the milk cells alone, Dandelion and Chicory can readily be 
•distinguished under the microscope. The milk cells stain more deeply 
than the surrounding parenchyma cells, and thus stand out conspicu- 
ously. 

Study longitudinal radial section of Dandelion and longitudinal 
tangential section of Chicory. 



58 Elements of Vegetable Microscopy. 

The milk ducts form a tangled network in the elongated parenchy- 
ma cells of the bark of the root. There are numerous cross-branches 
connecting the tubes. Latex varies in color in different plants, it may 
be white, or yellow, or orange, etc. In Bloodroot, it is reddish. 



CHAPTER XXIII. 
Lesson XX. — Vasal Bundles. 

The nature of a fibro-vascular bundle was considered in the lessons 
on wood and bast fibres and tracheary tissue, but the various types of 
bundles were not discussed. These will be considered now. 

According to the relative arrangement of the xylem and phloem 
masses three kinds of fibro-vascular bundles are distinguished, viz., 
collateral, concentric and radial. 

The collateral type is characterized by having the xylem and phloem 
masses lying side by side, with the xylem facing towards the pith or 
center of the stem, and the phloem towards the exterior. In the veins 
of leaves the xylem faces the upper or ventral surface, the phloem the 
lower or dorsal surface. Collateral bundles are characteristic of the 
stems and leaves of nearly all flowering plants. They seldom occur in 
roots. 

There are two varieties of the collateral type. 

The ordinary bundle containing one phloem and one xylem mass, 
and the bicollateral bundle, in which there is one xylem mass between 
two phloem masses, or vice versa. The second variety is found only in 
the stems of gourd plants (Cucurbitaceae), and a few others. Some 
collateral bundles continue to increase in thickness during the life of 
the plant and the growing layer is located at the junction of the xylem 
and phloem, forming a cambium or meristem zone of the bundle. 

Such bundles are called open bundles, while those which have no 
cambium zone and thus soon cease to grow, are called closed bundles. 

The open bundles are characteristic of the stems of woody dicotyls. 
An illustration of this kind of bundle has been seen in the Geranium 
stem, Lesson VII. The stems of most monocotyls contain the closed 
collateral bundles. 

Concentric Bundles : — These have a central xylem mass surrounded 
by a phloem mass, or vice versa. There is no cambium zone in this 
type. The bundle with xylem central is characteristic of nearly all 
ferns and club-mosses. The one with phloem central occurs only in 
stems and leaves of some monocotyls. 

Radial bundles :— In these the xylem tissues are arranged in radial 
masses and are separated from one another by the phloem masses, to- 
gether with some parenchyma cells. Such bundles are characteristic 
of the roots of all phanerogams and pteridophytes and stems of Lyco- 
podiaceae. 



Elements of Vegetable Microscopy. 



59 



The following scheme shows the types of bundles and their distri 
biition. 
Types. f 



Collateral bundles. — 
Stems and leaves of 
nearly all flowering 
plants, a few ferns, as 
the genera Ophioglos- 
sum and Osmunda, and 
stems of Lycopodiaceae. 



I. Ordinary bundles. 
— i. e., having one 
phloem and one 
xylem mass. 



f a. Open bundles. — 
Stems and leaves of 
woody dicotyls. 

i (Cambium zone pres- 

J ent). 

\ b Closed bundles. — 
(no cambium zone 
i present), Most mo- 
I nocotyls, the ferns 
I mentioned and stems 
^of Equisetacese. 



Co7icentric bundles. \ 



II. Bicollateral bundles. Chiefly stems of 
Cucurbitaceas (gourd family). 
f I Bundles with xylem central. Stems and 
I leaves of nearly all ferns, and club-mosses. 

II. Bundles with phloem central. Stems and 
t leaves of some monocotyls. 
Radial bundles.— Roots of all phanerogams and pteridophytes and 
stems of Lycopodiaceae. 

Collateral Bundles. 

Closed bundles. — Harden a stout piece of the stem of Spiderwort 
(Tradescantia Yirginica) in alcohol, and make thin cross-sections. 
(This is a monocotyl). Stain with phloroglucin. 

The greater portion of the section is made up of large ordinary 
parenchyma cells containing starch. Scattered among these cells, over 
the entire section, are numerous rounded areas of smaller cells contain- 
ing no starch. These are the closed collateral bundles. In the xylem, 
which faces towards the centre of the section, will be found from three 
to five thick-walled ducts, which in many of the bundles are arranged in 
the form of a V. In some of the bundles the xylem completely sur- 
rounds the phloem. 

On the side of the xylem towards the centre of the section, there is 
usually found a large intercellular space. This is common in closed 
collateral bundles. 

The phloem is composed of small cells which are mostly sieve cells, 
accompanied by some parenchyma cells. There is no growing or 
cambium zone between the phloem and xylem. {See figure 64). 

The bundles are enclosed by a single row of cells smaller in dia- 
meter than the other parenchyma cells of the section and containing 
little or no starch. This is the endodermis or bundle sheath. It is 
poorly developed in this type of bundle and is often not present at all. 
It will be met with later in perfectly developed form in the concentric 
and radial bundles. 



60 Elements of Vegetable Microscopy. 

Note the structure of the whole section of this stem. It is the type 
of all monocotyl stems. The bundles are scattered without any defi- 
nite order over the whole cross section, though they are more numerous 
in the outer part than towards the centre of the section. There is no 
true bark as exists in stems of dicotyls. 

Open Collateral bundles : — These are found in stems of dicotyledon- 
ous plants. In herbs, they are more or less isolated and the xylem 
portions do not form a solid continuous woody cylinder as in shrubs 
and trees. The cross section of the Geranium furnished an example of 
open collateral bundles. (See Lesson VII). 

To study the bundles in a woody type of stem make cross sections 
of the stem of Bittersweet, and stain with phloroglucin. Surrounding 
a central area of pith cells will be found a thick ring of cells that stain 
red, composed mainly of thick-walled wood fibres, which are inter- 
spersed with cells of much larger diameter, the ducts. This solid ring 
of cells is composed of the xylem portions of numerous bundles which 
have grown together and the only evidence left of their having once 
been separated is a number of radial rows of elongated cells running 
through the ring from the pith to the outer edge. These rows of cells 
are the medullary rays. The cells were once soft parenchyma cells 
between the bundles, but have subsequently become lignified. 

At the outer edge of the ring of wood cells is a narrow zone of 
small cells, thin-walled, unstained, rectangular in shape and more or 
less in radial rows. These form the cambium zone or growing layer. 

Outside the cambium is a zone of unstained cells, composed of 
sieve tissue and parenchyma cells. This zone is bordered exteriorly by 
a number of thick walled bast fibres. The area between the cambium 
and bast fibres, including the latter, is composed of the phloem por- 
tions of the bundles. The medullary rays are continued through the 
phloem areas. This region forms the so-called inner, or liber bark, 
spoken of in the lesson on bast and wood fibres. Next to the inner 
bark is the middle bark, composed of large ordinary parenchyma cells. 
Beyond this is the outer bark composed of a layer of cork cells. Only 
dicotyls have a true bark and the structure of such a bark is seen in 
this section. When the bark is peeled off, the rupture takes place at 
the cambium zone which is soft and easily torn. 

It is the definite arrangement of the bundles in a single circle, with 
xylem ends centrally and phloem ends exteriorly, that gives rise to a 
true bark and a central woody cylinder in dicotyls. (See figure 65). 

Study the whole cross section as a type of the more woody dicotyle- 
donous stems and contrast it with the stem of the Spiderwort studied 
above. 

Make cross sections of stem of Lizard's Tail as a type of herba- 
ceous dicotyledonous plants. 

Stain with phloroglucin. The bundles are arranged in a circle but 
are not grown together. They are separated by soft parenchyma tis- 
sue which forms the greater portion of the section. There is a cam- 



Elements of Vegetable Microscopy. 61 

bium zone between phloem and xylem. In the xylem, next the cambium, 
are some large ducts with a few parenchyma cells mixed in. Next to 
these are some ducts of smaller diameter and then a semicircular zone 
of thick-walled wood fibres marking the limits of the xylem of the bun- 
dle. In the phloem, next to the cambium, is a mass of soft tissue com- 
posed of sieve cells, parenchyma cells and a few secretion cells. The 
phloem is bounded by a layer of thick-walled bast fibres with pore- 
canals. This layer passes around to meet the layer of wood fibres of 
the xylem, forming thus a sort of sheath to the bundle. 

Note that the arrangement of the tissues in this stem is the same 
as that in the Bittersweet, the difference being one of degree rather 
than kind. There is far less wood in the section. The type of bundles 
and the arrangement in a single circle is the same. 

Make drawing of one of the bundles. 

Bl-COLLATERAL BUNDLES. 

Make cross sections of the hardened stem of Pumpkin, Squash or 
Watermelon. 

The bundles consist of a xylem mass between an outer and an 
inner phloem mass. In the xylem are some very large ducts, looking 
like large holes, with some smaller ones in the inner portion. There 
is a large quantity of small-celled parenchyma tissue. The phloem 
masses consist of large sieve cells and accompanying parenchyma 
cells. There are no bast fibres present nor any wood fibres in the 
xylem. There are two layers of cambium cells, one between the 
xylem and outer phloem mass, the other between the xylem and inner 
phloem mass. {See figure 65). 

The rest of the section is made up of very large-celled parenchyma 
tissue. 

Concentric Bundles. 

I. Variety with phloem surrounding xylem. 

Make cross sections of the rhizome of the Eagle Fern (Pteris aquil- 
ina) and stain with phloroglucin. 

On the exterior is the epidermis, brown in color, then several layers 
of thick-walled fibrous cells, also brown, known as the hypoderma. In- 
terior to this is a zone of large ordinary parenchyma cells with starch 
grains. Then comes a circle of bundles, separated from one another by 
parenchyma. The bundles may be round, or elongated, but never 
radially. Within this circle of bundles are two elongated masses of 
thick-walled, fibrous cells, dark colored. Lying between these are two 
bundles, elongated and larger than those of the circle. 

The spaces between the objects just described are filled up with 
parenchyma cells. 

In the centre of the bundles is the xylem composed of large scalari- 
form ducts, stained red, and a few small parenchyma cells. Surrounding 
the xylem is the phloem, unstained, consisting of a layer of small 
parenchyma cells with fine starch grains immediately next to the 



62 Elements of Vegetable Microscopy. 

xylem ; then a layer of sieve cells and their companion cells, finally 
another layer of small starch-bearing parenchyma cells. The bundle is 
sharply divided off from the surrounding parenchyma by a well de- 
veloped ring of elongated prismatic cells, known as the endodermis or 
bundle sheath. {See figure 67). 

There is no cambium zone in these bundles. All stems, such as 
those of monocotyls and ferns, in which no cambium exists in the bun- 
dles, do not increase in diameter from year to year, as dicotyl stems do. 
They remain slender. 

Note the plan of this fern section. It is the model on which all 
ferns are built. Note also that it differs from the monoctoly and dicotyl 
types of stems. 

II. Variety with xyglem surrounding phloem. 

Make cross sections of stems of False Solomon's Seal, or Sweet 
Flag, both monocotyl plants, and stain with phloroglucin. 

The structure of the bundles is just the reverse of that of the bun- 
dles of the fern, in that the xylem cells are on the outside and the 
phloem is central, but there is no endodermis present. In a few bun- 
dles the xylem ring is incomplete, and the phloem is continuous with 
the parenchyma outside the bundle. The concentric bundles with 
phloem central, may be regarded as closed collateral bundles in which 
the xyleTi has completely grown around the phloem mass. {Figure 67). 

Radial Bundles. 

These vary considerably among themselves in regard to the num- 
ber of xylem rays, and their length, the amount of lignification of the 
cells, the structure of the pericambium layer and of the endodermis. 
The number of rays varies from two to forty or fifty in different roots. 
The number of rays is indicated by the word arch with a numeral pre- 
fixed. Thus a bundle with two xylem rays is called a diarch bundle, 
one with three, a triarch bundle, etc. As a rule, dicotyl and gymnos- 
perm roots have fewer rays and a thinner walled endodermis than roots 
of monocotyls. 

Make cross sections of the root of the May Apple (Podophyllum 
peltatum) and stain in phloroglucin, (Dicotyl plant). In the centre of 
the section will be found the bundle, which in this plant is usually pent- 
arch, i. e., has five xylem rays, The rays are wedge shaped, with the 
broad ends toward the centre. At the outer narrow ends of the rays, 
the ducts are smaller in diameter, but are much larger at the broad 
ends, and mostly scalariform. The central portion of the bundle is 
made up of parenchyma cells, among which may be a few scattered 
ducts. 

The phloem masses lie between the xylem rays, towards their outer 
ends, and are separated from them by several layers of parenchyma 
cells. The cells of the phloem have glistening walls and may be told 
by these. The bundle is enclosed by an endodermis of elongated cells, 
which are thin-walled, as is usual in dicotyl plants. Immediately next 



Elements of Vegetable Microscopy. 63 

to the endodermis, are two layers of cells, larger in diameter than the 
cells of the endodermis, or of the phloem, and containing some fine- 
grained starch. These cells are known as the pericambium or phloem- 
sheath. The cells have the power of multiplication and root branches 
have their origin from them, opposite the xylem rays. {See figure 68). 

The area outside the bundle is filled with parenchyma cells densely 
filled with starch grains. 

Make sections of the root of Yellow Lady's Slipper (Cypripedium 
pubescens), a monocotyl plant, and stain with phloroglucin. The 
xylem rays are about eight in number, longer and better developed 
than in the previous case. They meet at the centre of the section, 
where there are numerous large ducts and smaller thick-walled cells. 
The ends of the rays are surrounded by thick-walled narrow cells which 
reach out to the endodermis, interrupting the pericambium layer in 
places. The phloem masses lie between the rays, the walls of the 
cells are thin and glistening. The endodermis is peculiar in that the 
cells opposite the phloem masses have their radial and inner walls 
much thickened, giving to these parts the appearance of a crescent, 
while the outer walls remain thin. The other cells of the endodermis, 
opposite the xylem rays, are thin-walled. This is a peculiarity of the 
endodermis of monocotyl roots. Make a drawing of the bundle. 

Compare with the section of cypripedium, one from the root of the 
corn plant, which is also a monocotyl. There are about fifteen xylem 
rays, somewhat like those of Podophyllum in appearance. They do 
not reach to the centre of the bundle. This is filled up with parenchyma 
cells, in which there is a circle of five very large vessels. 

The roots of monocotyls undergo very little change as they grow 
older, but, while the young roots of dicotyls present the appearance 
described under the root of Podophyllum, the older ones undergo rad- 
ical changes and assume the structure of dicotyl stems. In fact, the 
section of old dicotyl roots looks so much like that of a stem, that it is 
often difficult to distinguish it from a stem section. These changes can 
easily be followed by making sections of a root at various distances 
behind the growing point. 



CHAPTER XXIV. 
Lesson XXI. — Leaves. 

The leaf consists of i. the fibro-vascular system or framework of 
veins, 2. the parenchyma or filling, 3. the epidermis, which covers the 
whole leaf. The parenchyma or mesophyll of the leaf is arranged dif- 
ferently in different leaves, giving rise to two types of leaves, viz., bi- 
facial s.nd]centric. 

Bifacial leaves : — These are always flat leaves and in section pres- 
ent a distinct upper and lower surface, which are quite different in struc- 
ture. The parenchyma cells next the upper surface are compactly ar- 



64 Elements of Vegetable Microscopy. 

ranged and elongated perpendicular to the surface. Such cells are 
known as palisade parenchyma. They contain numerous chlorophyll 
bodies which give to the upper surface of such leaves the deeper green 
color, as compared with the lower surface. 

The parenchyma next to the lower surface is loosely arranged and 
scarcely elongated at all, and is known as spongy parenchyma. 

Most any flattened leaf will serve for the study of bifacial type. 
An excellent leaf is that of the Rubber Tree, (Ficus elastica) because 
of its toughness and thickness. Leaves bleached in alcohol will be 
better, as the sections will be more transparent. 

Make sections perpendicular to the lateral veins of the leaf and 
mount in water or glycerin. Sections of the fresh leaf may be cleared 
in carbolic acid or chloral-hydrate. 

The epidermis on both surfaces is composed of three layers of cells. 
This is not common to all leaves, but is usually found in tough ever- 
green-leaves. The triple layer affords greater protection. Here and 
there along the upper surface, and sometimes on the lower also, occur 
very large cells with a mass hanging from a stalk attached to the cell- 
wall, like a bunch of grapes, in the cavity of the cell. The hanging 
masses are called Cystoliths. They are not of common occurrence. 

Next to the upper epidermis, are two layers of elongated cells, the 
cells of the outer layer being much longer than those of the inner layer, 
and all are filled with chlorophyll granules. These are the palisade 
cells. 

The rest of the space below the palisade cells is filled in with 
spongy parenchyma. The cells are not elongated, and contain much 
less chlorophyll than the palisade cells. The cells next the lower epi- 
dermis are somewhat compactly arranged. 

In the lower epidermis will be found stomata or breathing pores. 
Some of the pores will be found cut'through the middle, giving a clear 
view of the guard cells. {See figure 6g). 

The cystoliths consist of a ground work of cellulose, infiltrated 
with calcium carbonate. On adding a drop of acetic acid to a section, 
the carbonate will dissolve with effervescence leaving the cellulose 
mass, which stains blue with chlor-zinc-iodine. 

At intervals along the section will be found the collateral bundles 
of the veins, with the xylem always towards the upper side and the 
phloem towards the lower side of the leaf. The upper and lower faces 
of a leaf can always be told by noting the position of the xylem and 
phloem of the bundles of the leaf. 

Centric leaf: — This type of leaf is symmetrical, i. e., the structure 
on one side is the same as on any other side. Palisade cells are not 
present. Centric leaves are terete, acicular, or succulent and occasion- 
ally flattened leaves belong to the type. 

Most any pine needle will illustrate the type, also leaves of Lady's 
Slipper, Sweet Flag, Hyacinth, Daffodil. 

Make cross sections of the needle of the Austrian Pine. If neces- 
sary, clear in carbolic acid, chloral-hydrate or Labarraque's solution. 



Elements of Vegetable Microscopy. 65 

The leaf is flat on one side, which is the upper or ventral, and nearly 
semicircular on the other. The epidermis is a single layer of thick- 
walled cells which possesses stomata on all sides of the leaf. 

Next to the epidermis are two or three layers of thickened fibrous 
cells, and next to these comes the parenchyma of the leaf, consisting of 
thin-walled cells, whose walls have been infolded, forming a variety of 
parenchyma known as folded. The cells contain chlorophyll bodies. 
Arranged at nearly equal intervals in the parenchyma, are about five 
secretion reservoirs, in which the circle of secreting cells is enclosed by 
one of thick-walled cells. 

A bundle sheath separates the central portion from the rest of the 
section, next to which are parenchyma cells surrounding two collateral 
bundles in the centre of the section. {Figure 70). 

Apply phloroglucin and hydrochloric acid and note result. 



CHAPTER XXV. 

More Important Test Reactions of the Parts of Vegetable 
Cells. (Bower's Pract. Botany). 

Cellulose cell-walls : — 

1. Colored faintly yellow by iodine. 

2. Swollen and ultimately dissolved by sulphuric acid. 

3. Colored blue with iodine and sulphuric acid. 

4. Colored blue or violet with chlor-zinc-iodine. 

5. Stained by solutions of carmine or haematoxylin, by methylene 

blue and in various degrees by other aniline colors. 
Lignified cell-walls . — 

1. Colored distinctly yellow by iodine and by chlor-zinc-iodine, but 

in case of bast fibres, the tint may vary to sherry-brown or 
even pink. 

2. Colored brown and swollen by iodine and sulphuric acid. 

3. Colored bright-yellow by acidulated sol. of aniline sulphate. 

4. Colored red with acid sol. of phloroglucin. 

5. Stained slightly or not at all by solutions of carmine and hae- 

matoxylin, but readily by aniline-colors. 
Cuticularized or Corky cell-walls : — 

1. Yellow by iodine. 

2. Yellow or brown by chlor-zinc-iodine. 

3. Yellow by strong potash ; on gradually warming (without boil- 

ing) bright yellow. 

4. Resist action of sulphuric acid, retaining their clearly-marked 

outlines. 

5. Are not stained by solutions of carmine or haematoxylin, but 

are colored by aniline stains. 
Mucilaginous Walls : — Resemble cellulose in many reactions. 
1. Swell with water and to a greater extent with potash. 



66 Elements of Vegetable Microscopy. 

2. Do not stain with iodine. 

3. Stain red with Hanstein's aniline-violet, blue with methylene 

blue. 
Calcium oxalate : -Occurs in cells in form of crystals. 

1. Insoluble in acetic acid. 

2. Soluble without evolution of gas in nitric or hydrochloric acids. 

3. Soluble in sulphuric acid, with formation of fresh crystals of 

calc. sulphate, if only small bulk of fluid be present. 

4. Are not stained with iodine. 

Calc. carbonate .-—Occurs as incrustations or crystals ; it is sol. in acetic 

acid with evolution of gas (CO2). 
Protoplasm or Proteids generally : 

1. Yellow or brown by iodine solutions. 

2. Yellow by nitric acid ; on addition of potash or ammonia a 

bright yellow color is produced (xantho-proteic reaction). 

3. Swell and lose details of structure on treatment with potash, 

ammonia, or Javelle water. 

4. Stain readily with carmine, haematoxylin, bright red with Han- 

stein's aniline-violet. 

5. Best stains for nucleus are haematoxylin, safranin, and methyl- 

green. 
Starch grains : — 

1. Blue with solutions of iodine in presence of water. 

2. Swell in potash, and in water above 65°C. 

3. Swell in dilute sulphuric acid. 

4. Swell and are colored blue with iodine in chloral hydrate. 
Inulin : — 

1. Soluble, but not readily, in cold water. 

2. Precipitated as sphere-crystals by alcohol or glycerin. 

3. Not colored by iodine, and soluble in potash. 
Fixed oils : — 

1. Black with osmic acid. 

2. Saponified by potash ; soluble in ether. 

3. Pink with alcannin solution. 
Resin : — 

1. Soluble in alcohol or ether. 

2. Red by alcannin solution and blue by Hanstein's aniline-violet. 
Tannin : — 

1. Deep brown by potas. bichromate or chromic acid. 

2. Greenish blue by ferric salts, 



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